The reason for complexity in computer systems (if we assume basic competence from implementors) is almost always a symptom of different people wanting different things. What feels like bloat to me is a thousand different wishes over several years.

Some architects decide to go with their own view and ignore the wishes that are against it. That might be fine and might be higher quality in some way but will also lead to fewer users which leads to fewer contributors which leads to less polish. SystemD might be complicated but that turd has been polished so much that it’s starting to be indistinguishable from a diamond.