The FIA weenies jumped at the opportunity to put out a neener neener statement blaming it on the FOTA members' refusal to go along with the FIA's proposed cost cutting regulations.
The real reasons? Given BMW's fairly business-oriented view of the world, their statement is probably not entirely smoke-screen, but I'm sure F1 leaving North America had an affect, as did the fact that they haven't done nearly as well this year as everyone expected. I read somewhere that the BMW heavies set a deadline for achieving the F1 championship.....they've looked to be headed rapidly in that direction each year, but their performance this season broke the trend and it wasn't going to happen soon.