can't you just imagine that a lot of people think that ruby is far more suitable/productive/readable to write applications than ObjC/Swift ? It's not just about learning this or that...
Concerning the translations you are talking about, it's completely trivial if you think the right way and don't just try to copy/paste things all the time. It's about objects, methods, interfaces, whatever the examples are written in...
Most people who choose this kind of thing are not experienced with the transpilation target, they're $language developers who want to avoid learning a new $language. But of course the main challenge when learning a new language is learning the standard libraries / eco-system, and these things don't help at all with that, they obscure it.
Another problem is that they never solve the impedance mismatch, idiomatic JS does not map cleanly to idiomatic ObjC, you end up with code that is idiomatic in neither.
"If I have to learn all the Objective-C / Cocoa APIs anyway" and "who want to avoid learning a new $language"...
Still not the issue, sure some people want to avoid to learn more, but that's not people we are interested in, those people wouldn't learn anything anyways... As you said, if you want to be very good yes you have to learn all the tools. So for good developers it's not about learning this or that, it's about learning both, and choosing the one you think is the best to write a full application.
", idiomatic JS does not map cleanly to idiomatic ObjC, you end up with code that is idiomatic in neither."
Sure, you end up with idiomatic RubyMotion. Is that an issue ?
Concerning the translations you are talking about, it's completely trivial if you think the right way and don't just try to copy/paste things all the time. It's about objects, methods, interfaces, whatever the examples are written in...