At the same time, privileged people will still sometimes feel a loss of something when you're portioning out a finite resource. So if a particular group is 25% of the population and they were getting 75% of the pie before and now they're getting 25% of the pie, that's a loss. It's a justified loss, but it's still a loss.

That said, there are other things like rights that are not finite in any meaningful sense of the word. When someone is feeling a loss because an oppressed group gained rights, it's usually because they're an oppressive asshole.