My personal explanation for this has long been that the computer and sensor technology is such that hand phasers are able to tell what their wielder is looking at, and also to optimize targeting based on a similar tech to what is used in some cameras today to determine where the focus should be.Hand phasers should have some kind of a means of manually aiming them(iron sights), but they don't.
It isn't a perfect explanation, but maybe they use the blade weapons because they can beat up or cut into opponents *without* doing much damage to the materials of a ship or station that they may intend to take as a prize?They seemed pathetic when they tried to conquer DS9 using blade weapons, how do these guys conquer any planet that made it to the industrial age?
As an aside to that notion, I'd really like to see a weapon introduced - Klingon, Fed, or otherwise - that is specifically intended for deck-clearing with minimum damage to the ship. Like something that rapid fires razor blades, maybe. Only problem is that if it's too good/effective, they'd play hell explaining why we didn't see it "later" in TOS, TNG, etc.