To the extent that your premise is correct: that naysayers are staying away....I don't believe I'm going out on a very brittle limb to suggest that many naysayers are searching for reasons to justify their saynays. Those same persons would have chimed in had Tesla revealed that the Model 3 was all steel, or all aluminum.
Now, during the ride clips that were posted during the Model 3 reveal, we heard that the Model 3 was a mix of both - there was zero specific commentary regarding how much of the body and how much of the frame/chassis was either. Each has its benefits and detractions: challenges to production, to compatibility with each other, to costs - both upfront and over the long term, to weight, to durability under variety of circumstances, to repairs....
I believe that your premise is flawed, which means no correct response directly can be made.