From an audience perspective everyone having the potential to wield the Force is more attractive.

These films were designed to appeal to children of all ages so gifting that audience with that potential (albeit fictional) is an aid to making an empathic bond with the protagonist.

We aren't meant to relate to nobility but look up to them. We are meant to relate to boy and girl next door characters.

Having it a skill that only a bloodline of mutants can do is sort of half there because the little kid in the audience may be able to imagine themselves a potential mutant lacking a Jedi Master.