I remember I left around that time too because they started aggressively trying to defeat adbockers. I'd rather just leave the platform completely than see a single ad.

Yeah but I think it just took some year for ppl to notice.

2013-2014 the algorithm got more foused on non-friend posts aswell as making the prioritzation less about "likes" from friends and instead some opaque engagement metrics. Groups had to "promote" post to get their prior reach to subscribers.

Also videos started to be posted around that time?

Tinfoil hat time but I think they definitely did _something_ at that time that "changed" the system. It's the Cambridge Analytica/Trump time and I believe that FB definitely "changed" at the same time.