Kjo wants power, it's all about ego - he needs to be known as the Kingmaker and have everyone falling over him. If he wants, people become successful, and vice versa. Alia gave him just that and listens blindly to him as well, unlike others he launched who can fall back on their parents and aren't totally dependable on him, or the likes of SRK/Kajol who he has always been on the backfoot with.
Kjo also needs to be with the younger crowd, he doesn't like hanging out with the older folks. Look at him tell the wives on the FLOBW show that he has FOMO that he's not on a group with Suhana, Ananya, etc. Everyone is replaceable to Karan, and I think he's been looking for Alia's replacement for a while.
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