Most were not disputed; some were, in fact, acknowledged. The hacked emails were also not nefarious or treasonous or illegal - they were embarrassing to the sender because they contained comments that would have been said differently - or not at all - for public consumption. And if you're honest, you'll admit that this is not only common, it is ubiquitous. 

There have been a number of news reports that GOP emails were also hacked, yet no content released. I find it extremely difficult to believe that there was nothing likewise embarrassing found in those hacked emails. WikiLeaks only chose to release those of Democrats.