This character has only existed for three years to less than stellar sales, I'm not sure why he would be expected to be part of the Spider-Man films at this point.
That's not entirely accurate. Before Marvel "killed" 616 Peter off and replaced him with the "Superior Spider-Man". Ultimate Spider-Man was outselling his mainstream counterpart. Superior Spider and Amazing Spider (now that Peter is alive again) sales are were/are stronger than Ultimates now, but in 2012 Miles was the main man.
Only because the book was riding the hype from them killing Ultimate Peter Parker and replacing him with Miles in the first place much like the stunt with SSM.