Basically guys…there are a number of reasons why Peter and MJ Post-OMD were written out of character.
Wanna know a big one though?
The fact that they
a) Weren’t trying to get back together and
b) Moved on
People forget…we’d literally been in this exact same situation before.
Mary Jane leaves Peter and goes to L.A.
For starters that event itself is out of character bullshit of the highest order because Mary Jane WOULDN’T leave Peter outside of something contrived like mind control, her going nuts, Peter and/or her fundamentally changing who they are, etc.
But more than this, at the start of JMS’ run, we saw that Peter, for however long it’d been after he and MJ had broken up (it’d been at an estimate at least a few months), was really not happy about it and upset. MJ was often on his mind, he didn’t entertain the idea of moving on and he (like her) were miserable and pining for each other.
They tried to arrange a meeting to sort things out that went awry.
Peter then tried to actually go to L.A. to talk to her about it. She needed more time to sort herself out (this was in the wake of her being abducted and held prisoner for months, so she was understandably a bit off kilter).
When Shathra went on TV and claimed she was having an affair with Spider-Man, Peter immediately called MJ to assure her it wasn’t true and MJ herself, even though deep down she didn’t believe it, was upset by the news. So upset in fact that she out and out went from L.A. to NYC to see Peter and again try to resolve things.
At the same time Peter changed his flight out of Ghana to take him to L.A. instead of NYC, again to talk to MJ. They both missed each other and deluded themselves into thinking the other had moved on and that they themselves should give up their efforts for reconciliation. Dejectedly both left to go home.
But upon encountering one another by chance in an airport stop over the two of them immediately dropped their plans to try and once again sort things out, which they succeeded in doing, getting to the heart of their relationship and making one another realise and resolve their issues (for the most part).
What I am trying to say is, given the situation from the start of Brand New Day, Peter and MJ’s actions are wholly at odds with what had already been established.
Peter and MJ both DIDN’T attempt any kind of true reconciliation with one another, despite in theory them remembering they’d been here before and knowing how they felt about one another and what they mean to one another.
Peter should’ve been trying to contact or see MJ to get her back and MJ should’ve been doing the same. They’d been through too much stuff to just let it go and move on. In fact, to quote one astute fan who abstractly touched upon this topic:
If he divorced, I honestly think it would simply be too emotionally devastating for him to be able to pick himself off the floor and try again. Because as I indicated in my Mary Jane series, it was a love that was built over time, tested, thwarted, and finally blossomed again when it was ready. After what the two of them have been through, there can be no other love for Peter Parker. They will all pale next to what he had in Mary Jane, and we will know that. No matter who he dates in the future, who he screws, they will all come in a distant second to her. It’s one thing to read a series about trouble, ups and downs, etc. – but what’s the point of reading about futility?
And that’s exactly it…Peter wouldn’t move on. And frankly neither would MJ. They’ve been through too much shit together.
Now granted in BND, Peter did still want to be with MJ as exemplified a few times, including the abominable One Moment in Time arc. But that just makes the fact that he DIDN’T try to truly reconcile with her all the more out of character for him. He even sort of tried to reconcile with MJ in the 1980s era of Spider-Man, where (despite being with Black Cat) thoughts of being with MJ cropped into his head, he flirted with her and later on he tried more than once to be romantic with her. In fact to a large extent during that run they were both effectively dating but in denial about it.
Peter and MJ should be much more upset and miserable over the fact that they are not together, not getting on with life and having it be this thing that kinda just happened as BND and Slott’s run have depicted them as.
And before anyone accuses me of saying all this stuff just because I’m a shipper, they effectively did the same thing with Aunt May.
Aunt May knew Peter’s identity before One More Day, and yet ever since then Peter has deliberately kept her in the dark with the writers just ignoring that elephant in the room. As such Peter has CONSTANTLY been out of character each and every moment we’ve seen him, in particular when he’s interacting with May.
If the writers ignored that and blindly pushed forward, I don’t think I’m out of line in saying they did the same with Peter and MJ’s relationship.
Ostensibly they are both of them out of character each and every moment they aren’t trying to reconcile, not actually together and are okay with both facts.