I'm pretty sure after the 30 ran, they were so well received and well done, they didn't want to quit, but they started calling them ESPN Films. It didn't have the same cache, so they went back to 30 for 30 the following year - even though it really doesn't make sense anymore. It's just a better brand.
BTW, I can't even find Grantland on that stupid new espn.com page anymore!