[WorldMaker]

I think there is an architectural problem, but not where you seem to be expecting it to be. I got caught up in some low level distro nonsense+drama from smashing my head against horrors deep in autoconf in automake and got a deep look into the realm of the Distribution Maintainer lifestyle and how much Linux distributions are individual snowflakes despite presumably all being the same OS. As the old joke goes "the only stable ABI on Linux is Win32".

.NET has a huge kitchen sink standard library. Maybe the closer parallel is Python and Python has had periods where it only supported a few named distributions, too. That's not currently the case, but "how the sausage is made" is still a lot grosser than you might expect, with some Distribution Maintainers maintaining entire forks and a lot of the work not done by Python directly. Python is everywhere because it became one of the favorite shell scripting languages of Distribution Maintainers. (Which also exacerbated the Python 2 to 3 migration because entire distros got stuck on 2 while all their shell scripts got rewritten.) (But also if you want to compare Java's cross platform to .NET's I think we need a long digression into how many Java runtimes there are and the strange and subtle incompatibilities of different distro's affiliations to one or another. I also made the mistake of trying to use a Java application as a regular application in my youth of accidentally dealing with deep distro incompatibilities. That was also not fun.)

I get it, you don't have to like .NET. I just think you have an inflated view of what "cross platform" means when it comes to Linux. Linux isn't just one platform. Most things are rebuilt from source constantly because the binary interfaces especially libc's/glibc's under them are constantly shifting like quicksand. See also the messes that are Flatpak and Snap and how much work they've done to try to build around distro incompatibilities (by building increasingly more complex wish-it-were-VMs).