We want to get the money in sooner than later, cuz some cards are going to kill our action on the turn. If a flush makes on the turn, and Villain's holding a J, a pp, or a straight draw, he's less likely to put more money in the pot.
The other thing to consider is that alot of guys will convince themselves that you must be bluffing
, since w a paired board it's unlikely you're holding one of the other two K's - so you may be pushing TT's or something, which means my J is good!!!
That's not to say it's never correct to slow play, but on a wet board like this I think it's a mistake to slow play - I'd rather slowplay KK5r than this board (tho I admit slowplaying isn't really a big part of my game... ).