I just don't like it. It's not that I'm incapable of doing the math, or that I can't find a calculator online. I just don't like pointbuy.
I think it's b/c I end up putting a lot more thought into my stats than I normally do when rolling. When rolling, at most you're prioritizing, usually, which is a lot less fine-grained than spending points. And, sometimes, I find myself with either a good or a bad roll that I end up putting somewhere and that helps define the character more. I end up thinking "oh, ok, he's like this now ..."
I play plenty of point-buy systems, but rolling, usually 4d6 though I can see the appeal of rerolling 1s, that's my preference for D&D.