For one, nitty players.
As many have noted, bluffing has many benefits: everything from balancing range to table image. Do I bluff? Yes. More than I should? Maybe. For me, it really depends on the opponent/table though. Like others have said, some players are just not bluff-able. Many of them are beginners who are calling stations and bluffing against them is seldom ever a good idea. When I bluff, it is usually exploitative - especially if I have live reads on them.
I understand the few players that only semi-bluff. However, against the right player at the right spot - I could bluff with ANY two cards and make it work. Bluffing is a paradox in the sense that the more you do it, then the more likely you are to get called. Even a beginner will realize that you've bet every pot and can't have THAT many good hands, right? Bluffing less can make your selected bluffs more believable. I embrace table image though. If I get caught bluffing, then I adapt. Maybe they will lose a big pot to me because they just saw me bluff last time. Who knows?