Not sure if you also mean mom/daughter without the step. I dig the mom/son roleplay but I never watch anything labelled stepmom unless I know the 'step' is dropped in the scene. Stepmom does nothing for me and I rather they just made a regular video then.
I've found that the step-whatever is the most overused thing in porn these days. As a see it it's a middle way for content creators to get those on board that dig actually roleplays and not scare those off that are not into the fully committed actual roleplays. Imo they just end up satisfying no one that way.
The step-whatever is of course also a way to keep payment processors at bay.
In any case for my part I'm fine with all the step-whatever is dropped as long as we get actual roleplays (like the Penny Barber and Lexi Luna ones) on a more frequent basis.