The problem is Wikipedia being misleading again. They each support a proc filesystem. There is no single the proc filesystem that they support.
A case in point: FreeBSD's /proc is very different to Linux's /proc, and most of what one would go to /proc on Linux for is obtained via sysctl() on FreeBSD, with a lot less in the way of machine readable → human readable → machine readable busywork formatting and re-parsing involved.
A case in point: FreeBSD's /proc is very different to Linux's /proc, and most of what one would go to /proc on Linux for is obtained via sysctl() on FreeBSD, with a lot less in the way of machine readable → human readable → machine readable busywork formatting and re-parsing involved.