>>108089967Jessica Drew, Anya, and Julia carpenter have all had their push and they never garnered a large enough fan base to continue pushing. Mayday may have numbers, but she's also a 'definitive' end to Peter Parker's love life. Even if she was from an Alternate dimension, her constant presence would be a reminder to the public of "Why isn't Peter Parker fucking MJ so May can happen?"
Spider-Gwen has popularity among the masses right now, and while that hasn't exactly translated into decent comic book sales for her, she has a much better chance than any other variant of Spider-woman (besides mayday).