Were they rejected outright or did the reviewers ask for revisions? In my own field, it is very rare for the first submission to be accepted outright. The vast majority of papers are sent back with suggestions for revisions before they are resubmitted, and those suggestions are not consistent across reviewers. I am not suprised at all that new reviewers would send an already published paper back with suggestions for resubmission.

Think of it this way. If you took an already published book and submitted it to a new editor you would get a list of suggestions of how to improve the book before it is published.