There's also likely a (c), which is people who don't think that Facebook should do anything about it. I guess that could be considered part of a set with (a), but I thought it should be mentioned separately as it's a different motivation.

Might I suggest (d): analysts, disgusted by the fact this crap is on top, tweaked The Feed in an attempt to disfavor that type of content then ran a simulation but saw their simulated ad revenue become lower than allowed minimum, then did (a) and went out to have lunch.

“It is difficult to get a man to understand something, when his salary depends on his not understanding it.”

- Upton Sinclair

In particular, stare too hard at that viral page, realize how scummy that page is, and then spend the rest of a career at facebook trying to tear down the systems that made that the most viral page, are likely going to earn you enemies, and cause the company to lose money (in the short term, at least).

Did you stare at that page on Facebook? The top post has millions of comments.

Which is totally fair in my opinion. It is no single individual's job to fix an issue this big and I don't think it's even feasible for a single person to do at a company like this. And if management hasn't set up incentives for people to proactively fix issues like this then they probably won't get fixed. Upper management can and should fix these issues but they probably don't care because they don't think it's an issue.