What you get with P2F is people who have rich parents. What you don't get is people who have the best skills and drive to be the best pilot they can be. If it's all handed to you on a plate, why would you need to be so driven? I know someone whose parents were plenty rich enough to pay for him to study full time. Even so it took him almost two years to get his writtens because, frankly, he just wasn't that bright, even though he's a nice enough chap. Anyone self funding would have had to give up long before then.
It's not dissimilar to the current situation with UK Universities. Those from a privileged background get to go, even if they're not the brightest spark. Those from less privileged backgrounds may go, but leave with crippling debt that for the long term leaves them on the back foot. Then there are those who are genuinely smart, with incredible aptitude, who just plain and simple can't raise £50k - £100k just like that. I would rather hire someone who really wanted it in their bones and was really skilled and knows how to work hard.
Seems the airlines would choose quantity (of spare cash) over quality...