Early-stage cultivation progresses rapidly, making one very powerful, but once reaching the Foundation Establishment stage, progress will be limited by one's innate talent and become slow, wasting time.
He only accepts one disciple because he needs only one person to study the cultivation methods of the people in this world.
Additionally, he can only care for one person at a time, reestablish their foundation, and ensure their path after Foundation Establishment is smooth.
While cultivation relies on personal comprehension and opportunity, he doesn't want this group to enter the cultivation world only to find no progress and end up dying in a foreign land.
"Then, senior, can we enter your world on our own?" Elijah asked reluctantly.
If only one person is accepted, what about the women of Azure Isle?