It might because, Erynn is kind of the first ex and she has drama associated to her like all the exes in other games, while Iris doesn't have any drama, and MC was attracted to her because she felt very similar to Erynn. Iris is kind of Erynn by proxy for MC, even though she is far more wild.lol just realized something that I find a bit funny. Typically I love getting back together with EX's in other games on at least one save unless they horrible people. Yet I like Erynn more than Iris, Erynn even feels more like a ex to me even tho she isnt one lol. For whatever reason Iris never interested me at all in this game other than on a chaos / manwhore save. Tho she isnt on the LI list as far as I know either but still I find it a bit funny since any other game she probably one of my favorites lol.
Meanwhile Alexis fucks a guy she's never dated and has met for the first time in 5 years after just a few minutes talking to him, yet you seem to be implying that she's less slutty than Erynn.
Alexis clearly does it only with MC. She has tons of other opportunities in college and in the bar, yet she doesn't hook up with anyone else. We don't really know her dating history though. Obviously, she had at least one boyfriend, and she had sex before several times. MC is exactly her type, and they connect immediately, it's love at first site, even though she already knew him from before, and she envied Erynn's relationship with MC, and MC is her first kiss...Yet Alexis sleeps with the MC within 5miniutes and multiple other times
The only thing that felt weird was that she only wanted sex for a while, instead of having a serious relationship, but we quickly learnt that it was because of Erynn. Otherwise, she might not have jumped on MC and instead try to have a normal relationship with a normal pace.