Except most "normies" don't even know who Miles Morales is. This character has been pushed very hard from the start by all the usual subjects (i.e. USA Today giving him the "Best Character of 2011" award or some other nonsense, which probably didn't exist at that paper before or after that; SJW's in media sites acting like he's the greatest thing in the history of comics and must be "the" Spider-Man). Even now his book is selling around 30K and heading down into the 20's. As Jim Shooter pointed out, that would have got his title cancelled a long time ago. And I'm guessing a lot of that is over-shipping by Marvel.
But Miles Morales as the declared "Black, Diverse Spider-Man of the future instead of this white guy" was instantly a huge cause for the far left, so they -- which includes the producers of this thing -- have to push him at all costs. That's why we have a Spider-Man cartoon on Disney XD, and yet Miles has been forced into it as another "Spider-Man" after only ten episodes (Disney also wants to sell more toys, if possible). It's why they set him up in Spider-Man: Homecoming. It's why Miles Morales is getting his own movie instead of an animated film with Peter, the real Spider-Man, as a college student or an adult, or a *married* adult which we've never seen yet.
So the Miles Morales "popularity" has been manufactured from day one -- a concoction that's been pushed by certain people of a certain political persuasion for a single purpose: replace Peter Parker for being a white hero -- or at the very least strip him of being the one true Spider-Man. It's why Christopher Miller and Phil Lord want to sell the idea of "anyone can be under the mask," even though we all know it only works for the long run if it's Peter under there. The goal is convergence and for Miles to replace Peter -- and nothing will get in the way of that for these people. That's what this "Legacy" nonsense is all about.