Could also be that with Ultimate Spider-man being a thing right now, maybe they felt using MJ here would be redundant or would undercut the main 616...
I always thought of Jean as more of a parallel to Gwen Stacy than MJ. Especially as portrayed in the 60s as a more "traditional" female archetype and...
It's in line with other piece of information and evidence have - like the fact that Peter and MJ were always the most popylar couple, that MJ coming...