Alot of times when actors aren't on a shortlist, its because there usually isn't a shortlist because the director of filmmakers have one person in mind which is what happened with Affleck, Ledger, Hardy, Downey, Keaton, Stewart, Mackellan, etc. That's usually when you get the " No one talked about them!" reaction because the filmmakers focused knew what they wanted already so tests and shortlists weren't needed.
There are rumored actors in the media who are allegedly shoe ins for a part such as Bryan Cranston for Lex , which don't come true, but that's because they never were in contention anyway.
When you usually have a shortlist of actors , one of those actors is usually chosen. Maguire, Bale, Garfield, Evans, Hathaway, Collitlard, Craig, Franco, Dunst, Stone, etc were on shortlists and were chosen. Now of course , anything is possible, and casting happens alot of different ways. In this case however, given the multiple sources which are pointing to certain particular actors for the Spiderman part, its unlikely imo we're gonna get some dark horse out of left field choice.
Even if it isn't Asa or Tom , the actor is likely gonna be very similar in age and background. So we could be surprised, but its likely the chose is gonna be 18-20 years old even if it isn't Asa or Tom.