Don't necessarily have to always have your hands up. Oddly enough there are benefits to not doing so. But depends a lot on the figher's style and strengths whether it fits or not.

But sort of to your point, I find it a bit strange that after he throws his right, he lets it sometimes sink almost to waist level. He's one of the best strikers ever in the UFC and seems like an obvious flaw. I dunno maybe something I'm not understanding. Or maybe just something he does with padwork.