It's a Hall of Fame.
Some figures get their fame from winning races, owning legendary teams, great media work, or just having a great story. Allison came from racing royalty and was a huge name that was on the course to superstar status. Edwards probably will make it in, but I wouldn't vote for him, I'm okay with him eventually making it in, but on the pure performance scale he should be the cutoff. However, the HoF isn't solely based on performance, and that's perfectly fine.
Allison (and Kulwicki) both fall short in terms of on paper results, but that isn't everything. The Hall of Fame includes not only drivers, and is not meant to be an objective meter to rank careers. These names have stories attached to them. Everyone has their personal opinions on what is worthy of making the hall, but making it an 100% Hall of Merit is impossible and a waste of time. If that was the goal, the induction process would look far different.
There's nothing wrong with getting in the hall solely based on the story they either "wrote" or were apart of. The names Davey Allison and Alan Kulwicki mean something to hall voters, and a lack of on track results due to tragic circumstances shouldn't be used against him. Davey has more fame attached to him than Edward's. Not either of their faults, it's just how it shakes out.