FFP’s are a win-win for Universal. If they didn’t have them it’s not like the majority of guests would pay for more than 2-3 days anyway. They increase revenue and crowds which in turn drives demand for Express passes.
If you look at the pricing Universal pushes people who may only be planning 2-3 days into FFP. I’m sure the thinking is they aren’t going to be spending any more than that on admission but they might get a little more out of them on food, merchandise and possibly hotel.