I have two main guesses:
1. Min Heejin wants full creative control over the app. Maybe the layout and some features will change to match the aesthetic of different comebacks.
2. Since the members are so young, ADOR wants to be able to properly monitor what happens on the app. If something goes wrong like glitches, anti-fans, alleged harassment, etc, they can get to it immediately without waiting for the weverse team, who also has other groups to monitor.