For the past 15 years, mobile has been the main revenue source for Facebook. As big as Facebook is, they're at the mercy of the 2 competitors: Apple and Google. Apple has been very hostile to Facebook, because Facebook make a shitload of money off Apple's platform and they refused to pay a certain percentage to Apple - unlike Google who is paying 20B a year to access iOS users. Apple tried to cut Facebook off with ATT on iOS 14, but it didn't work.
Because of this, Zuckerberg has to be incredibly paranoid about controlling his company destiny, to stop relying on others' platforms to deliver ads. It would be catastrophic for Facebook to not be a main player for the next computing platform, and they're currently making a lot of money from their other businesses. Zuckerberg is ruthless and he is paranoid, he has total control of Facebook and he will use all the resources to control the next big thing. I think it comes down to this: Zuckerberg believes it's cheaper to be wrong than to miss out on the next platform, and Facebook can afford to be wrong (to a certain extend).