Agreed, and I think it's mainly because it gets hard to figure out what content to display when 1) people are following 300 friends + 300 pages; 2) advertisers

Agreed, and I think it's mainly because it gets hard to figure out what content to display when 1) people are following 300 friends + 300 pages; 2) advertisers are paying for their content to be seen. The competition for a spot in the users' news feed makes it increasingly harder to present the user with quality content...I sometimes wonder how it's even possible to test the quality of their algorithms a such a large scale (kudos, btw), even with all that automated continuous learning.