Margaret was someone Alex didn't want.
She was too naive for Alex to let her be with him.
Yes, Mira was also naive, but unlike Margaret, she would kill anyone her instincts called dangerous.
Margaret, on the other hand, would try to find good in her enemy.
It was a quality that got her kidnapped a lot in the story.
In the plot Alex knew of, Keryu saves her, but because of that, her personality remains the same, becoming one of the few weaknesses of Keryu, an overpowered protagonist.
Alex didn't want that.
He didn't want her broken because Margaret was good only because of her personality, but he didn't want her in his harem either.
The solution was simple: give her to Ben.
That guy was a protagonist who grew with every challenge, so Margaret, a trouble magnet, was perfect for him.
If that wasn't enough, after integrating with Keryu's memories, Alex now knows Ben's real identity; he knows that the safest place for Margaret would be beside Ben.
