Comment by pdpi

"Bad" comes in many shapes and sizes. Specifically, "technically competent person implementing a thing designed by a technically incompetent person" is remarkably different from "technically incompetent person implementing a thing designed by a technically competent person".

The way this plays out in practice is that those products you listed can hire actual UX designers, but many product decisions are made by people focusing on business concerns rather than product concerns, so you have competent people implementing designs by incompetent people.

Inversely, because open source software is usually built by people trying to scratch their own itches, they those people actually understand what the product should be, but, because they're usually software engineers instead of UX designers, they're typically incompetent at UX design. So you have incompetent people (devs with their UX design hat on) implementing designs by competent people (those same devs, with their "scratch my own itch" product owner hat on)