Also, Hulk was creating an alternate timeline by removing them, meaning that if he brought them to his reality and never returned, the Ancient One's divergent timeline would be left unprotected. Presumably Dormammu would have conquered that Earth, if something else didn't first. I think the Ancient One's exchange with Hulk was very loosely inspired by Hickman's "Incursion" buildup to SECRET WARS, with different realities potentially pitted against each other for survival. The Ancient One was saying that what was good for Hulk's reality wasn't necessarily good for hers.