Why would you do that to help this bluff along?

By raising the flop, you're representing that you flopped a big A, a set, or two-pair. You're not representing that you have a drawing hand. My instinct is that by raising the flop, you're more likely to get called if the draw hits because the raiser is not likely to conclude that the draw was the hand that you are playing.

In addition, you are also giving the raiser a chance to re-raise you and take away the pot odds that would make it correct to play the draw.

Thus, it seems to me that a raise on the flop is a bluff calculated to take the pot down on the flop because you sensed weakness rather than to set up a bluff later in the hand if the draw presented hits.