They use poor quality materials and the repairs often fail much sooner than factory panels. Need to get the rust out from between the panels. They probably didn't use any seam sealer and the crud got inside the seams. To have it last you should repaint the whole thing since it is already failing with rust bubbles on the panel.

My neighbor bought a new truck in 2000, garage kept and babied, got hit and had a fender replaced years ago. Paint has failed and looks terrible while the rest of the truck that got the same treatment looks like new.