No one wants a polyamory relationship. That's just a weird way to get two vanilla paths in one playthrough.
We want a throuple. We want Jaye and Mallory to desire one another as lovers, not just friends, and for that lust to amplify the sexual tension and release in an AVN. They are both shown to be bisexual, so there's little reason to think this should not be possible. It was the job of the writers to have them develop feelings for one another through their shared experiences and connection to MC. This never happened. Instead, the writers chose to have the girls react differently (in terms of their relationships) to essentially the same set of life events depending on whether or not the MC fully commits to one or the other. I get that jealousy and insecurity are real things - but this isn't a story grounded in reality and never was.
If the writers felt that these kinds of interpersonal driving forces should heavily feature into their story, then they should have done so consistently throughout. MC should have been angry at Jaye and Tara upon learning of their sexual relationship (I mean, they're still best friends, why wouldn't MC feel jealous?), Jaye should have dated others while MC was away and probably had found a new relationship by the start of the story, Mallory and MC should not have put up with Amanda's non-consensual antics, Jaye should have been upset about MC continuing to text with Fiona, Erica should have been angry at Linda for cheating on her dad, Jaye and Mallory should have been angry about MC kissing Bianca in front of them (instead of both getting +love/trust points) when confronting the uncle, MC probably should have been turned off hearing about Lisa fucking her cousin (great date night talk, eh?), etc. Luckily, this was not the case, because that would not have been entertaining, which is ultimately what an AVN is about.