[api]

This is correct. The Linux desktop works, but the last ~10% of polish and UX attention is what takes like 95% of the time. It's the little things, the edge cases, the things that just sort of work or break at odd times or in odd ways. The parade of edge case issues that must be fixed to make something really high quality is endless.

That sort of polish is the least fun aspect of programming. It consists of brutal iterative bug fixing, polish, design tweaking, and repeat. It's endless. Since this is the part of programming that is not fun, people rarely do it for free. Linux desktop has basically no economic model so it has no way to raise money to pay people to do the nasty grinding work required to make it truly competitive with a commercial OS.

The other huge problem is unnecessary fragmentation. There are like six popular desktop distributions that are all fairly similar under the hood. There aren't any fundamental differences between them sufficient to merit a fork. So you have to distribute your app many times to target one platform: Linux.