Let's be real, it's a more descriptive term. Plus it isn't slang like SJW (and in many circles a slur). So yeah it's a better term when discussing these things.
I don't think any SJW would characterize their position is the dictionary definition of regression, and nor would I (despite not characterizing myself as one). Do people you consider SJW really say "life was better before?", I instead hear "life was bad before and is better now but hasn't gone nearly far enough: the trajectory of political correctness and minority rights needs to progress drastically further forward on that same line drawn from 1950 to 2018". It seems very difficult to attribute that sentence to the textbook definition of "regressive".
If a political position was literally "let's go back to how things were" then it would be fair to call that regressive. The closest thing I can think of is MAGA though, and for most other cases the goal of calling something regressive seems to clearly be "your politics will make things worse" not "your politics will return things to a previous state".
Whether you agree or disagree, I believe that the people who consider some SJWs to be “regressive” is that the system used to be that social conservatives used to tell people what to think, we had a period of open-minded exploration, and now SJWs are advocating moving back towards a system that people are told what to think, except it’s social liberals who are doing the telling. In the sense of someone telling people what to think versus a embracing a wide range of different views, it could reasonably called regressive — perhaps up one level of abstraction if you want to get technical.
Note that I am not supporting one view or another, rather I am just explaining how the term can be used to reflect one’s perspective accurately.
