Even well before Occupy, /b/ had the Scientology protests, which attracted a lot of undesirables. They eventually moved off-site, but the damage was done. Every time 4chan ended up in the MSM, more shitty people showed up. The large majority of /b/ didn't want this IRL activist bullshit on the board. They wanted to troll, not "change the world" or whatever do-gooder nonsense the activist newfags wanted to do. And yeah, we saw the same problem with Gamergate and the 2016 election. /pol/ was still fun in 2013 because most oldfags from /b/ had moved there to have fun with things like the Zimmerman trial and Dorner manhunt. But the election was the final nail in the coffin for /pol/.