They just aren't good enough down low. Great guard play but Val is huge bitch (will improve in a few years, I still believe), Johnson is playing like garbage, Patterson isn't really a post presence, and Hayes is just too damn old/small.
They need to acquire someone realistic like Al Horford or that big Eurotrash guy from the T-Wolves who can dominate down low.
There has also been talk about Greg Monroe from Detroit being on the block, he'd be a great pickup.