> Bug bounties are supposed to represent a high probability payoff of a lesser amount of money for finding a bug. This is in comparison to going the black hat sales root, where probability of sale might be lower, but the payoff might be higher. I can imagine one or two state actors who might pay top dollar to have keys to the kingdom to a major social network. (https://news.ycombinator.com/item?id=10756159)
Expected payout = (Probability of reward * size of reward) +/- any additional value I put into who I'm selling it to.
If I have an exploit that gives me a lot of access to Facebook (or any other large company) I have to run that formula for each entity that might pay me for it- Facebook, the NSA, the Chinese Military, and so on down the list. Facebook is offering high probability for a lower payout. The NSA might step up their game and start offering ten times as much, or make it more clear that they will indeed pay you for it (not that I have any proof they'd do such a thing).
Make no mistake, Facebook has probably done this math very carefully when choosing a bounty.