Uh, no, they can’t make literally anything they want. I’m sure they would rather make a Star Wars TV show because that has a massive pre-existing audience, but they don’t have the rights to that. They could’ve made something original, but that wouldn’t have any pre-existing audience at all.
And I’m not necessarily levying these complaints against the showrunner himself. I don’t think he’s some greedy corporate suit, I’m sure he loved the Bethesda Fallouts and jumped at the chance to make a TV adaption of them. But let’s not pretend that the reason everything nowadays is a reboot or remake or sequel isn’t because of purely financial motivations.