Okey, here's a theory for why Disney is pushing Kylo Ren especially.
They want to establish Star Wars as "Disney Princesses For Boys", but out of the human, young characters Kylo is the only one who's white and male, and because they're still racist, misogynist shitheads that's the character they push on all the boys.
@Tobi i think this is accurate, with an aadditional dose of "he has a striking aesthetic with an unusual lightsaber and mask" that makes it easy to merchandise and design things around him