On a grassroots level, where each server is small, the people who run it are more invested and have more direct control over it. That in itself provides better quality.
Twitter can't do the same because it's a vast corporation whose job is to make money for its shareholders. It doesn't care about anything else.
If you want a real world example, who is more committed: a small family that own a restaurant, or some random people at a random branch of McDonalds?