Besides those points above me, I'll also point to the female protagonist representation perspective as an up-until-recently untapped market in this general isekai boom. And by female protagonist, I mean girls that act like girls, not what (often male) authors thinks girls are like or want girls to act. And the stories also tend to be more social-focus than power-fantasy.
The "clearer life purpose" and clearer story directions in general can be seen in the story descriptions, where isekai stories are often "I got powerful (relatively or just blatantly) effortlessly, so I'll do whatever I want", while villainess stories are often "I don't want to die (literally or figuratively), so I'll use social skills to avoid that" and/or "I don't like the direction this story is going, so I'll go away and live on my own". The isekai ones are much more flexible wish-fulfillment, but require setting up the world and characters the readers would care to see more of and empatize with, which can be difficult when the protagonist can do "whatever they want" and can easily be made too powerful in too vague ways that the readers don't even know when they're in trouble or not, while villainess ones are mostly grounded in normal world and the troubles are mostly social, so the readers can quickly recognize what the protagonist can and can't do, and thus easier to emphatize with the characters.
