The ATF has a system of points to determine the eligibility of a weapon for import. A certain number of points are given to each feature that is deemed to make a firearm more "sporting." There's a chart depicting it here
Glocks barely make the cut in standard service calibers. The .380 chambering doesn't.
For what it's worth, the prohibited models aren't any smaller than their 9mm cousins, so their market viability is questionable.