Most people who play these games/VNs will likely be pursuing all the girls they can, not just one, because that's how most guys are; they want many different women without (much) consequence and these games let them live out that fantasy. So, to keep interest in the game for as long as possible, it can be very beneficial to allow players to continue having multiple relationships right up until the end, or near the end.
DPC can very easily keep all these relationships going until the last few episodes, even if the players have to make choices between certain girls that unlock different scenes, but there's no reason why we couldn't still be dating/seeing Maya, Josy, Sage, Jill, and Bella, with the occasional side pieces like Camila, Riona, Lily, Jade, etc.