The more people you are connected to the less of their posts you see. Its simple maths – the more people you are connected to, the more posts will be sent to you. But given there are still only 24 hours in the day, you have less time in which to see the posts, so you miss most of them.
The majority of posts never get seen, let alone read. Social sites like Facebook only serve posts based on your historical behaviour with previous posts – cue the banjo music.