I come from traditional "unix hacking" background and don't know at all the JVM or .NET ecosystems, and share the irrational distrust of them many unix hackers have, though I'd get over it I could actually get stuff done faster with them. But some projects I do are lower level or need high performance or reasonably small staticly linked binaries, or instant startup time (cli utilities), so rust is a better choice. For most of the rest a JVM or .NET language would be fine and should be more productive as it's a higher level language, but I don't know if I'd use it enough to learn the language and ecosystem and tooling enough to be as productive as in python or rust which cover pretty much anything I need to do at the moment.
I think that is also why rust ecosystem will keep expanding and improving a lot. They said about python that it's not the best language for anything but 2nd best for everything, which isn't really true as python can't be used when you'd need C or C++ but rust can really be used for anything.
(TL;DR: The JVM was NOT "the epitome of open-source" for many years and it's still struggling with the knock-on effects of spending so many years being one of the only things that you couldn't install through your package manager for purely legal reasons.)
Second, I can't remember which blog post it was, but Eric S. Raymond has mentioned that the reason he found Python much more appealing than Java is that Java's standard library embodied an attempt to push people to write portable code in ways that made life difficult when your goal was explicitly to do POSIX-specific things.
As a Linux user who saw C# for the "Microsoft's take on Java after the Visual J++ lawsuit" that it was and, thus, never really saw any interest in it, I can say that C# gives that same impression of "ill-fitted for POSIX-native stuff" (packing its CLR bytecode into .EXE files doesn't help, even before you get to the assumption that you'll have Wine and Mono fighting over who should open .EXE files when double-clicked.)
Rust, by contrast, produces truly native binaries, has Cargo come standard and makes `cargo add libc` or `cargo add nix` trivial and reliable, etc. etc. etc.
Third, the JVM's tunings, optimized for long-running processes, and the start-up time and approach to memory allocation that resulted, gave it a reputation for being slow and bloated. The POSIX ecosystem has a history of encouraging composition of short-lived processes via shell scripts.
Fourth, Java has always let the quality of the GUI experience on X11 languish.
I still remember how you needed to set environment variables to work around "Java applications produce empty grey windows under non-reparenting window managers" for years and years.
I still remember when you had to open part of the JVM in a hex editor and replace XINERAMA with some nonsense string that doesn't match anything to un-break Java applications on multi-monitor systems.
TO THIS DAY, I still can't find a Java GUI widget toolkit that doesn't have a noticeable responsiveness/input latency problem under X11.
(Swing, SWT, JavaFX... that annoying fraction-of-a-second sluggishness is one reason I'm planning to write my own replacement for the parts of the new JavaFX-based version of PlayOnLinux that I actually use once I stop using the old Python version.)
I haven't tried QtJambi, but given that SWT, which should be using GTK on the backend, exhibits the problem, I don't hold out much hope.
(In essence, in the same way that Swift is ill-suited for stuff outside Apple devices, .NET has gained a stigma of "ill-suited for anything outside Microsoft platforms" (Is Unity's Linux support still only viable for targeting it, not developing on it?), and Java similar, but for JavaEE servers... and since your average POSIX developer sees AbstractThingFactoryBeans as a tired but too-accurate joke about what hell it is to write Java... you do the math.)
“Since this article was first published, Sun (now part of Oracle) has relicensed most of its Java platform reference implementation under the GNU General Public License, and there is now a free development environment for Java. Thus, the Java language as such is no longer a trap.
You must be careful, however, because not every Java platform is free. Sun continues distributing an executable Java platform which is nonfree, and other companies do so too”
Also, Stallman is quite an “extremist” and he is often himself the enemy of open-source by his gatekeeping, so there is that.
Re the GUIs: I think it says a bit also about the state of GUIs on linux, then the reverse - and I say that as someone who has been using linux on every computer I own since forever.
You made some great points, but I think the real reason is even simpler, old graybeard linux users are very conservative in their technology takes. The overabundance of C software (and the unavoidable memory vulnerabilities that come with that) even at places where it makes zero sense is clear sign of that, but so are the “systems/pulse/wayland hater fangroups”.
First, note that I also pointed to Java spending years developing a reputation as one of the only things you couldn't install through the package manager for legal reasons.
People who don't care about Stallman's zealotry do still care about that and it presented a similar lasting problem to Java's Linux uptake as the problem D had more broadly with two competing and mutually incompatible standard libraries (Phobos and Tango) in the early years.
As for the GUIs, I listed three different ways unique to Java that Java GUIs were subpar on Linux:
1. Needing weird workarounds for applications to not display blank grey windows on non-reparenting window managers. (Basically, if the WM was something like a tiling WM that didn't reparent it from the root window to a WM-provided "titlebar and borders" parent window, the app would refuse to render anything without enabling the relevant hack.)
2. Caring so little about solving known bugs that slipped through QA that, for a shamefully long window of time, users with more than one monitor literally had to hex-edit their JVM to intentionally no-op the XINERAMA detection to make applications work. (i.e. XINERAMA being the X11 extension that allows Windows/Mac-style "one desktop stretched across multiple monitors" multi-head instead of the older "Behaves like a software KVM and applications are trapped on the monitors they opened on" Zaphod mode.)
3. Having some kind of input-response latency that I've never seen in another language or toolkit, which is apparently caused by something so fundamentally Java that it's present in every Java toolkit I've checked.
As far as greybeards go, I think we'd need more data points. Eric S. Raymond is quite an old-guard guy and even had some "jumps to conclusions"-y, "it's not enough like C"-ish reasons for choosing Go over Rust (eg. No `select` as part of the standard library, ignoring how Rust intentionally keeps the standard library minimal), but had no problem with using Python where it was suitable, while he didn't like Java because it was was more of the ChromeOS or Android school of doing stuff on top of a POSIX base.
I think that is also why rust ecosystem will keep expanding and improving a lot. They said about python that it's not the best language for anything but 2nd best for everything, which isn't really true as python can't be used when you'd need C or C++ but rust can really be used for anything.