I wouldn't purposefully give them bad
gifts, necessarily, because bad gifts are a waste of money all around, but I might not spend as much time and effort on finding just the perfect gift for them. I wouldn't feel motivated to go all out, if you know what I mean.
Are you sure that there isn't some other reason for this? Could they be having financial problems, and just aren't able to afford lavish gifts for everyone? In this case, I still don't see why they wouldn't get a less expensive but equally thoughtful gift for everyone, but it's worth suggesting, I guess.
Are these gifts a problem because they're bad gifts, period, or because they're regifted? My brother and SIL gave us regifted presents a couple years ago (I know this for a fact because bro had previously offered me one of the gifts we were later given, but it must have slipped his mind
), but since they were gifts that we would have liked if they'd been purchased, we figured it didn't make a difference to us. BF and I had a good laugh about it later, though. If they're regifting just to get rid of junk, I'd be offended, but if they're regifting thoughtfully I wouldn't be.