But the problem with add-ons is that every machine you use will have a different combination of them installed. Maybe you're at work and don't have privileges to install them. Maybe you forgot to install one on your desktop even if it's on your laptop, etc.

And building it into "a lot" of Ubuntu-based distros lacks discoverability. I might have that now on the machine I'm typing this on, but it does me no good if I don't know it's there. (Everything in Linux has worse-than-terrible discoverability, but that's another rant entirely.)

MS's dominant position meant their defaults Just Worked everywhere, and when those defaults were good, they were really, really good, by virtue of their ubiquity. Then they fucked us by using their dominant position to just... I don't know... completely lose the plot? Aside from HiDPI fractional scaling and support for large monitor "maximize to a quadrant" and stuff, I can't point to a single MS UI improvement since the XP days. Everything else has just gotten worse, fragmented, and for no good reason.