They're running scared.
Edit: And as things stand, I'm having trouble seeing how Core actually raising the cap themselves isn't the most likely scenario. At this point the choice for Core is
- compromise a fairly trivial amount, to 2MB, *now* and retain most of their market share and at least a nominal degree of influence
- lose a massive amount of power as Classic takes some/most/all of their market share and they end up raising the blocksize cap in a few more weeks to match Classic anyway
I would prefer the latter as that recalcitrance by Core would cause maximum decentralization of development, but I'm pretty sure Core would prefer the former.