You've given an good example, but it doesn't really fit the situation. Val has just appeared, compairing to Elena & Lexi for example, no one knows her, friendship lasting for one month and for several years is not the same thing. Layla & Elena are besties for years, Layla & Lexi are sisters. It's a first major part and difference in situations and their possible outcomes. Then it comes to the second part, which is also intertwined with your next quote. Regarding this particular game , it's plot, story and universe - we are only allowed to get closer to Elena if we're doing well with Layla.
Nyx written and made it this way. Elena is opening and warming up to MC while seeing how good he is treating Layla. Because Elena knows that Layla have issues and still in trouble after Lucas case. And Elena have her own issues and "situation" too. If MC is not interested in Layla - they aren't getting close with Elena enough to make her being interested in MC as well. Elena & Layla are protecting each other in different ways. Elena's protection lies in a way to control how particular guy treats Layla as a girl (take Zach as example). She kinda looks after her. While Layla's help and care of Elena is more mundane or better to say practical. She knows her family and social/financial situation quite well and help her in different ways. The most frank example and one that was shown and hinted to us - that she is sharing clothes with her. At such particular period of life and girl's age it means a lot. Imagine Elena w/o Layla around and and all alone - poor thing.
And I think this particular friendship and their whole relationship is written quite well and deep enough to bring player different reasons and emotions and make this final choice complicated enough.
The thing is... story is good and can touch and bite you in a different ways only if you can somehow relate/believe/trust in it. Life is complicated thing as well as any kind of relationships.
If the game story makes you feel like shit after doing something bad to imaginary character(s) - then it's written good enough. It means that you kinda care about story and it's characters and you have invested more or less emotions into it. And following a "clean" single LI path is not a guarantee of drama free path and pass if story is really well done.
Finally, we have enough range of reasons to play/watch/read something and different goals at the end or during this process as well. Signs of a good product (in our case - decent AVN game) that you interested in story and plot and you care about characters. Or you (and others) write something like this on F95 and other forums and chats.
Someone just wants to distance a bit (or not just a bit) from real life, someone wants to experience something that is not available to him in real life, someone wants to feel certain emotions or their spectrum, etc. Simple desire to just jerk off can't be forgotten as well, but I think the games like this particular one is not compatible with it, since focus is not on sex and lews scenes as is, but on relationships and bringing different emotions to player first of all. First sign of game which is intended as a pure jerk off material - no characters conflicts, no real feelings and emotions while playing. Just juicy pictures and scenes, harems, zero consequences, even little ones or they mean nothing or lead to more and more sex rather than making you feel bad/uncomfortable/guilty etc.