Because in the end the game is about MAX. From what has been said in the past (EVIL Scum) Eric will HAVE to go for the game to progress. As things are now the two characters MAY be friendly, but they BOTH want ALL the ladies for THEMSELVES. Eventually, Max will remove the EVIL from the house in order for NEW things to happen. If (EVIL Scum) Eric remains the best anyone who plays the 'Friendship' path can hope for is a loop and NOT getting new content. If Max (the MC) is removed the game ENDS. At some point the only way for NEW things to happen will REQUIRE things to CHANGE (Eric must go).
As I said, Max is the MC, (EVIL Scum) Eric is an opponent. One will eventually have to win, which means the other MUST go. If the roles were reversed, then the result would be the SAME. Winner stays, loser leaves. My understanding is that there WILL be some content locked behind the friendship path as Max 'Learns' new things, but that WILL end eventually.
I hope that explains the situation as I understand it.