I'm not necessarily sure if it's because there are more shares or just because there isn't as much original content.
Ultimately for me facebook has become a lot less useful as more people are on it. It used to be mostly my siblings, a few immediate friends and some of the more tech minded people i knew from work. That was great, I could ask a technical question there and have a discussion about it. Now if i post something like that the first response is usually "lulz i have no idea what you talking 'bout", so I don't bother with stuff like that. I use dropbox to share family photos with my immediate family since I don't want them to have distribution as wide as facebook. I know I *could* set up privacy rules to maintain that stuff better but I can't be bothered.
I strongly believe they are in a downward spiral and think it'll be hard to claw back from that. As the utility it provides to me drops, there's less incentive for me to provide value to them.