That's really the issue with games like that. When you have multiple characters, every character will be *somebody's* favorite. So every time you release an update, and in that update not every character gets some new content, somebody will be disappointed. There are only three potential ways to make your audience happy in this situation:
1) Keep the character roster small and therefore manageable, which makes it less likely for too many people to be disappointed at once (MM already failed at that, with the amount of side-girls);
2) Make sure that every update has something for every character (again, falied);
3) Make updates small, but frequent, so that people don't even start questioning if the game is abandoned (failed yet again);
And before anybody starts that discussion again (particularly with point 3) - it's possible to work on big events in the background, while still releasing small updates along the way.
everytime they make a game like this, and you see them starting to add 10+ girls, you know it will end this way, its same with so many other games, why cant he just do, i dont know, 5-10 events focused on a girl, release, and then work 5-10 on the next?
maybe do a couple of events to 5 of them, 2 main girls, and 3 side girls(or 1 event for 6 girls).