P2P also gives developers the chance to plan in the long run, because they have a certain amount of monthly income just from the monthly fee alone that they can plan with.
I'm not saying it's impossible to make a fun, enjoyable game with a F2P model, but the likelihood of things going well and especially of big, groundbreaking new systems getting introduced over the passage of time goes down by like 99%.
Oh, and something else:
The price of one month of FFXIV playtime equals the price of one cinema ticket for one person, not including drinks or popcorn. Basically that means if I have even just 2 hours of enjoyable playtime per MONTH, it's already worth it.