I don't know if I agree with this one. Have you seen any of their more recent Iron Men in-hand? They are extremely complex and impressive, in some ways similar to the way the Endo is in that they are engineered so well. They do have some drawbacks though in that all the Stark likenesses suck, and they completely upgrade their Iron Man figures with every release, essentially making previous ones obsolete. It really is a line meant to have little staying power, which isn't the case so much with other lines, though we have seen lots of re-releases in the Terminator and Batman lines.Iron Men are the most toyish and simplistic looking of Hot Toys entire output. They don't show the best of their talents, which is why its hilarious that they make up the largest portion of what they sell now.
As for why folks haven't picked any. . .those guys don't leave the Marvel section