I think it comes down to this statement which, admittedly, only holds true 70-80% of the time:
Those who have played older editions, or started before 4E was introduced prefer PF to 4E. Those who started since 4E began prefer 4E to PF
4E is easy to get into from a complete outsider's perspective. PF has more rules it seems, more rules interactions, and more difficulty (all from an outside perspective)
PF is close enough to 3E that those who played them have little to relearn (sometimes). To go from 3E to 4E there are many rules and ability changes, many more then 3E to PF.
In short, older gamers stick to what they know(PF) while newer gamers find whatever is easiest to start out in(4E).