This is just not true. You can still write GTK2 or SDL apps, you just need to package your app for the target distro or open source it because it's an open-source-first ecosystem.
If you're looking for binary stability and to ship your app as a file, ELF is extremely stable. If your app accesses files, accesses the network through sockets, and use stable libraries like SDL or GTK it will work fine as a regular binary and be easy to ship. People just don't want to write their apps in C, when the operating system is designed for that.
Many native apps like Blender, Firefox, etc ship portable Linux x64 and arm64 binaries as tar gz files. This works fine. You can also use flatpak if you want automatic cross platform updates but yes, the format is unfortunately bloated.
It's not that easy to ship a JavaScript app on other OSes either and electron apps abound there too.
What does ELF being stable or people not writing apps in C have to do with Linux binary compatibility? No matter what language you use, it’s either dynamically linking to the distro’s libc or using Linux system calls directly.
Also, I recommend taking a gander at what the Linux build process/linking looks like for large apps that “just work” out of the box like Firefox or Chromium. There’s games they have to play just to get consistent glibc symbol versions, and basically anything graphics/GUI related has to do a bunch of `dlopen`s at runtime.
Flatpak and similar take a cop-out by bundling their own copies of glibc and other libraries, and then doing a bunch of hacks to get the system’s userspace graphics libraries to work inside the container.