I believe it would lead to fewer chances for the mites to migrate between colonies - i.e. more flowers == less bees per flower == less chance for a mite to jump from a bee to a flower to a bee/different hive.
That's just a guess tho and my gut also says that climate change isn't helping.
Probably a lack of good information - with only a hundred odd cases and not having had much time to get the facts, I'm betting that's a SWAG (scientific wild ass guess) and we'll have better info the more time has passed.