Its not only that Facebook is probably planning an ICO, but that they are really trying to clean up their ecosystem. The bitcoin related advertisements fell into 2 categories:

1-ICO scams: most of the coins advertising on facebook had no product and crappy whitepapers. Is it any wonder that the biggest one was bitconnect?

2-Get rich quick schemes: James Altucher carpet bombing your feed with his "secret formula" for cracking the code on crypto currencies. Im sure FB received a lot of complaints about those and i am extremely happy to know i won't see his face 50x a day...