Because Berman and Braga are a couple of talentless mooks. They were the driving force behind TNG, Voyager and Enterprise. DS9 Was Ira Steven Behr and Ron Moore, who wrote most of the TNG Klingon episodes that you like. Moore moved on to Voyager, but was frustrated by the insistence on writing TNG-style stories instead of trying something new, so he left. He went on to create the new BSG, which is basically the show that Voyager could have been if they'd had the balls to do it.
I'm wary of casting too much blame on Berman and Braga (as seems to be popular). There's a bunch of evidence that there were a lot of cooks involved in Voyager and Enterprise (whereas DS9 was largely left alone by the network).