I'm not saying this to bash open source translations (let alone translators) or anything. A good translation takes a lot of work. That's just how things seemed to be last time I tried, and I don't really have the energy to contribute myself nowadays.
Of course there are other reasons for not using a localised desktop especially if you're a technical person, such as better web searchability in case of problems. But the inconsistent quality of translations is probably one of the top reasons for me.