Facebook has features like intelligently improving the quality of your feed, being able to hide posts from certain people, prioritizing posts (not just stacking them based on their age), calendar/birthday stuff, events, chats, etc.
Twitter is just a never ending stream of information, not prioritized and always overflowing with too much content (at least IMO).
I think Facebook nailed it with realizing their engagement levels are directly related to the quality of the newsfeed, and because of this they put a great deal of effort into making it as relevant as possible to each user. They realize that if you friend (or follow) somebody, you're not necessarily interested in ALL of their content, but maybe only their most interesting or popular. They also realize that if you only log in 2 times per week, they should prioritize with the best recent content, not just the stuff that was posted 1 hour ago.