I honestly think the FFP's has matured enough that airlines (some of them anyway) can feel fairly confident in the amount of data that has been collected to do lots of analytical slicing and dicing to come to the conclusion that they have left money on the table, or at least feel like they are giving away too much.

More simply put, they are getting more greedy thanks to all the ways technology has now enabled them to understand their customers and market. The US airline industry, in its current state, also allows them to get away with it.

I'm sure there are additional operational/economic pressures to squeeze the FFP from a loyalty-based model to one that is based purely on revenue reward, but the key enablement to do it now vs before is their ability to make those calculations/forecasts and the industry consolidation which does not give customers many options.