So I've been wrong the whole time.
I've always noticed that Crowley never bothered to learn people's names, but I always thought he basically liked being around people and enjoyed that aspect of the work.
And I thought Aziraphale found people annoying (customers are the worst part of owning a bookshop) and just wanted to be left alone to read.
Turns out, Aziraphale's the extrovert. He knows everyone in his community. He likes them. He wants to hang out with them. He wants to perform (badly) on the stage, host a party, help people -- always, he wants to help people. It's central to who he is.
And Crowley's the introvert. He wants everyone to leave him alone. He wants to be with his plants and his car and Aziraphale and that's pretty much it. He will find some enjoyment in helping others but, now that there's no Arrangement, he's not interested in going out of his way. He just wants to be alone with Aziraphale, a universe of two.
It's easy to see why they can't work it out yet.
I am just surprised I didn't see it before. It was always there.