Market share/popularity correlates directly to amount of available software, and their support. So it is completely rational to care about these metrics.

I care about other people having to suffer a shitty computing experience.

It is a little funny that I can't tell if this comment is pro or against desktop Linux.

Could be both tbh. There are definitely ways in which Linux is better - no ads (cough Microsoft) or artificial restrictions (e.g. recording desktop audio cough Apple).

But in the most important ways - software availability and reliability - it is much worse.

Reliability for sure, though it has gotten better. You could argue that availability is better because it's all free, but I see what you are saying. Often enough I can't use a program natively on Linux.