It's possible it has nothing do to with bloodlines. Of course, different races, species, and parts of the galaxy do have bloodlines, so that's not really an argument against bloodlines. We also know that people can make it into adulthood without any knowledge that they have the force (Leia, Rey), so it's for two non-Jedi to have a force sensitive child who becomes a Jedi. So it's not simply a matter of Jedi having kids. Given that there has been a long period of time from the end of III to at least the end of VI in which Jedi were not active, at least two generations of force sensitive people went unidentified.
I guess what I'm saying is that we don't know enough to rule out the force as an inherited trait.