Luke didn't have to have any kids and neither did Ben. There is no gun to anybodies head to procreate and if there is, seek help. But in this franchise it's not like the force can't procreate and Luke simply had a kid that just sat out the sequel trilogy.

If it's a power thing, well power had nothing to do with either continuities initial death of Palpatine. Vader happened to be standing next to him and a pit. The chosen one prophecy just required Palpatine be killed, it didn't require Anakin to be Superman. And then it's not like most people could tell you who the Legends descendants are aside from having a cursory knowledge of Mara Jade. Most people will only ever know about the movies and maybe a couple of games and comics. And that being said it's still not like we can't get adaptations of them. Rey being descended from Palpatine impacts next to nothing with Cade Skywalker aside from an asterisk on the wiki page.