Games that try to force more than one playthrough especially feel like a chore if the only difference is that
on play 1 you get girl A, but on play 2 you get girl B. And that's what most non-harem games end up like. You went with girl A to the cafe in that run, but the movies with girl B in this run! So different,
Even AAA games with millions of dollars and teams of devs that have multiple endings often only get played once by most players. Statistically most players don't replay games that are story based (Edit: or any games really, even strategy game like Total War and such often don't get the majority of players to keep playing them after beating a campaign with one faction). Not to mention that even those can botch the ending being different, relatively even in gratification, and all are impactful. Looking at you Mass Effect 3. And even story games that do have dedicated player bases, like Skyrim, most players replay and make the same choices because those are the choices they like, the story they want is the same, they just try different builds or challenges, and they may have never even tried a different ending or choice in a story moment.
But some AVN devs seem to think that they will make girl B's date at the movie so meaningful and so different from girl A's date at the same movie theater (since its the only daz asset they probably have

) that players will obviously want to play the whole game again.
And all of that is before even get into what FatGiant brought up.
This is how a lot of non-harems just play like harems for a huge chunk of the game. Which on one hand makes sense, the devs want you to have seen all the girls before you pick one, but they also feel like they each need a sex scene too because they see AVNs as porn often (which they aren't they are erotica), which ends up giving an incongruent experience. And it ends up begging the question of why make the player pick just one girl after that? They always give excuses like "realism," or "character reasons," but you already violated both of those by having the "Try before you buy" experience in the first place. Most guys irl don't get to fool around at the same time with 4+ (let alone the higher numbers that some games that still force a choice have) girls and then pick one like that, and most chicks aren't going to be down for that either if they aren't down for that, as in if they wouldn't also be fairly easy to convince that they should just keep the same status quo going since it works. Most guys are lucky if they can get one girl at a time. Especially in the modern era where a lot of chicks are using aps and something like 80% of chicks are hooking up with 20% of guys and about 60% of guys between 18-30 are either virgins or have only had 1-2 sexual partner their whole life. So, if you've got the Mc that can land more than one chick at a time anyway, and you've chicks that are already willing to be in a de-facto harem anyway for much of the story, then why wouldn't you just have a harem route?
Anyway, ramble over,