Why did Bulldozer disappoint? Some possible answers
 

AMD's "Bulldozer" microarchitecture has been something of a disappointment, particularly in the FX desktop processors, where it doesn't consistently outperform AMD's prior-generation Phenom II chips. Since Bulldozer is the first full refresh of AMD's primary x86 architecture in many years, we've been left with lots of questions about why, exactly, the new microarchitecture hasn't performed up to expectations.

http://techreport.com/discussions.x/23019