I always imagined that Force powers was like being a muscian or a martial artist..anyone can play chopsticks or throw a punch or kick but only a few can be beethoven or bruce lee.
Being a jedi knight IMO just meant that those people had dedication and a gift much like jimi hendrix who literally slept with his guitar which meant he practiced ALOT and had a gift of music as he was self taught.
No one says that chopin had bacteria in his blood and thats why he did what he did musically so why not that kind of thing for jedis??