It's the way the trailer and screenshots for DOAX3 focus squarely on body parts, the way the characters created to market DOA5 to an otaku audience are now front and center, the way any pretense with the framing story is dropped. There's also the agency of the characters. Trailers for older games show them generally having fun on their own terms, while the key video we have for the new game is strictly about encouraging the player to leer at them.
Compare the websites for the current and previous game:
https://www.gamecity.ne.jp/doax3/
http://web.archive.org/web/20100728142447/http://www.deadoralive.jp/doax2/index2.html
Oh, yeah, and then there's the boobie mousepad bonus item for the limited edition. DOA never stooped to that level until DOA5 (as far as I know).
The point is that you used to be able to distinguish between DOA and more porn-y games. You can't really, anymore. Totally unscientific illustrative graph: