I know that. But it was considered before than too many Phoenixes might now want to accept our offer if they have somewhere on the Plane of Fire they feel they would be more needed. I'm proposing we market the Imperium as nice place to raise kids. Down to a nice fire aligned hatchery demiplane and tons of plucky kids for their children to grow around.Phoenixes lay eggs when they choose to, when they feel they can feel they have the time to instruct and help a young phoenix phoenix grow. If any of them feel they would be better served on the Plane of Fire than the material plane they will say so and go back, it's not like you are compelling them to stay.
If some of those baby Phoenixes and kids get along enough to become Phoenix touched Mage and familiar? That's just another plus.