Probably most of the folks willing to experiment in assembler have been discouraged for so long it will take a while before arduino is seen as assembler tolerant. ARM adds some interesting new variables too (though nothing that can't be handled with a big enough ifdef).
Of course studio has some essential features for this sort of development, like port stimulation files and step-by-step debugging and monitoring cpu/memory, but I just thought it would be nice to throw those results into arduino easily because the whole thing doesn't need that level of development, nor do the people using it, and since it is alpha, it is easier to share at the project level (cut and paste), I could then easily offload the controller portion of development. Though there is a lot of marketing influence here too, I'm just doing this for fun, and I find wringing the most value out of minimal hardware "fun" 