Because there is no single "default instance that is always a good choice and wouldn't go down randomly because of lack of funding". That's both a strong and a weak side of fedi

How is the fediverse different. Can't the owner of an instance post as you? Can they read all your data stored on their instance and pass it to anyone they want to?

Higher friction and fragmentation are Fediverse features (not bugs) that give it a different grain. ATProto has different tradeoffs that lead to a different form of social media. I'm glad both exist, and bridging efforts are worth paying attention to for anyone frustrated with the distinctions.