Curses were sealed and grew with the Soul. As the Soul grew stronger, the Curse slowly loosened one restraint after another until it finally awoke. That way, it was possible for Cursed Children to survive the immense pressure exuded by Curses.
If Michael inserted a Curse into Alice's body, she would be torn apart. The Curse would merge with her soul and awaken instantaneously without giving Alice – her soul – the time she needed to adapt to the Curse's power and pressure. Even if Alice refined her Soul to the peak of Tier-5, she was unlikely to survive.
Of course, there were exceptions. Alice's soul could be much stronger than the norm and, therefore, resilient enough to endure fusing with a Curse, but the rewards weren't worth the reward.
