1. The priest who is responsible for the propriety of the Mass in his parish and honestly cannot do so or permit it because of his own inadequacy in Latin.
2. Altars lacking room to stand in front.
3. Vocal parishioners. (I've been floored by the vitriol I've heard almost every time the word "Latin" is spoken in liturgy meetings and classes.) Not a lot. But it doesn't take a lot.
4. Bishops who lead by example ... in not using either Latin or ad orientam.
5. Peer pressure. "Older and wiser" priests who caution against this passing fad.
6. Peer pressure. "Older and wiser" priests who have been banished from parishes because of their attitude against anything post V2 and "[I]t's d***ed well about time you asked me to say Mass as it should be said. Oh. And no women on MY altar." (And the resultant bad taste the experience has left in everybody's mouth.)
7. Priests who are still praying for the right Spiritual guidance to progress.

What I've seen preventing the adoption is a lack of demand, mixed with "no one else is doing it". There are deeper ecclesiological reasons, but that's the basics: Priests might want to face the altar, but facing the congregation is, like it or not, now the norm. And a priest who isn't inclined to doing it won't because no one's putting the pressure on him. Same goes with Latin. The #1 complaint about Latin at my last church? "They don't do it at St X!"

I've always thought that the relationship to the older liturgy has a lot in common with how generations of immigrants deal with the new language and culture. Those who immigrate will always be more familiar with their old culture as much as they embrace and identify with the new one. The second generation, feeling somewhat embarassed by their parents' foreign ways, try to disassociate themselves from their parents' cultural heritage and try to become completely homogenized. The third generation begins to scratch their heads and wonder about what has been lost from the old ways, though they sometimes can't even speak their grandparents' language as their parents never taught it. Right now, most priests are in this second generation-born before the deforms...err...reforms but ordained after them. Latin is the shameful, backwards-looking language of the old generation. I think that trying to change the minds that have been this way for 40 years is a losing battle, and retraining and reeducating will not alter what is a sociological phenomenon. God bless all priests and may they enjoy long lives, but eventually, these second-generation priests will no longer be bishops and pastors.

I'm kind of caught in the middle on that one. I do like Latin and prefer the EF over the OF any day. But, I am a Byzantine Christian, and the custom in the east is liturgy in the vernacular. Consequently, I do what the norm happens to be in the parish where I work.

Ioannes, I think Fr. Z said at one point that a lot of people only have one big change in themselves, and a lot of these priests who are old enough to have gone through the reforms just don't ever want to do it again.