It's a common tactic because it throws a wide net for everyone to find "their girl." The dev wants to give you a lot of options, so you will get invested in at least one or more of the girls and keep playing. It doesn't matter if the storylines are completed, just that you come back for the next update.
You could also look at it as a positive if the dev is receptive to feedback. I like the idea of starting the game with a lot of girls, then finding out who the players like and going from there. It's like super smash brothers. There's a character for everyone. But, again, that's assuming the dev actually cares about player feedback.