I read somewhere on the forums that the new pp system works so that it weighs your best performances more heavily and if you FC a song that doesn't yield enough pp to warrant a spot on your best performances list (or close to a spot) then you're not going to get a lot of pp, if any.
IIRC the method is something like: you have a list of scores that give you 100pp, 99pp, 98pp, ... weighed by a factor of x that decreases exponentially down the list.
In this example, your total pp would be T = 100 + 99*x + 98*x^2 + ...
So if you FC a song that gives you 50 pp, for example, that would rank ~50 on your list which is weighed by x^49. Assuming x is around 0.9, that's 50pp * ~0.005 = ~0.25pp.