The real reason behind this new decision is that Mark Zuckerberg is planning to release his own cryptocurrency. There is a hidden plan behind the curtain that is slowly revealing itself alone to the potential investors. I don't think that other developers will be very fond of this because with current capital and technology facebook could make a breakthrough on the market. Other ads that are currently promoting designated cryptos are a threat currently to the Facebook because if Zuckerberg plans really to release his own crypto promotion of other crypto is the first step to start his potential plan.
Here is a link to an interesting article about the possible Facebook cryptocurrency:
https://hackernoon.com/facebook-could-launch-the-ultimate-cryptocurrency-2e6a5b65665bThis is possible and is unfair. Facebook will surely succeed due to its large network and their popularity.