JAL this can also be viewed the other way around. If the player does not reject JM, i.e. chooses the romantic path for both, he is still forced by DPC to interact with Sage, Isabella and Jill.
This is exactly where I see what DPC is getting at. He wants the player to decide on his LI as early as possible.
The later the player decides, the more complicated the friendship is likely to become and the jealousy factor that DPC introduced (I believe in EP7) will strain the LI relationship and friendships.
The example below is from the JM path. I don't have any other path. But it shows the pattern of DPC.
My MC has no romantic interaction with the other LI's.
Jill: My MC helps Jill with tennis against Tybalt and the concert. But he can't and won't help Jill on her third date with Tybalt. What is the consequence. Jill stands up and shows Tybalt her cute raccoon teeth. Conclusion: The MC has boosted Jill's confidence. This is going to be a great friendship.
Isabella: The MC convinces and permanently proves to Isabella that he is a decent young man and not the pervert who ran around campus naked. She also sees him helping Jill. Summary: At the end of the concert, Isabella gives the MC a friendly hug after saying that it warms her heart what great friends Jill has. Yes, Isabella was damp with the hug. But not because she was excited about the hug, but because the ice queen's ice shell is melting.
Sage: Needs a real friend more than anything. From the scene of EP5, I conclude that Sage's experiences with boys have always been the same. Falling in love quickly, horny sex, and then bye-bye. She probably never had a real boyfriend. So it's all the more important that the MC stands up for Sage and Maya during the walk in the woods. Did you see Sage's reaction to this. Just fantastically portrayed by DPC. After that reaction from the MC, Sage knows that the MC is her best friend and will remain so whether she can help Maya or not.
In short, this is to show that there can be a happy ending if the MC is and remains a decent guy. There will be no jealousy with and among the LI's because there is simply no reason for it. But that's what Zoey is on her way to the MC for.