If I were an attorney what a field day I'd have with these designers. Since I'm not, I'll simply say that they own the copyright to the printed materials, meaning that I can't copy and sell them as my own work. They can't copyright protect anything else. And they really need to get a clue because all they're doing is alienating potential buyers.
Right now I'll buy a pattern I like as a courtesy to the designer. But I'm close to the point where if I read "you can't reproduce for resale" blah, blah, blah one more time, I'm going to stop buying and simply recreate the work to the best of my ability without a pattern. Which in most cases is darned easy. The real joke is that many patterns are so poorly written and designed that they really aren't worth the copyright protection that does cover them.
And for the record, I've never sewed and sold anything in my life -- but I don't like being told that I can't if I want to when I've paid for something.