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.