Hi,
Last week, I saw some here in a botanical garden.
The trees are big -large and high- and not very productive in quantity - for the one(s) I saw ... That might be a reason for them not being more cultivated.
Regarding cross-pollination, I couldn't be sure if there was one lone tree or 3 grouped. But they had some fruits on the floor under their branches.
Just for you to be sure, I'm outside your continent :) in Europe. Pawpaw are not grown here except for some in botanical gardens.