How does anyone make money in limit holdem?

[bocablkr]

Sorry if this has been asked before but I am usually only a NL player. I make decent money at NL holdem, both live and online, because I can occasionally bluff someone off a hand and I can also protect my premium hands from getting out drawed.

However, in limit holdem I am an average player. I can never protect my great hands - AA gets cracked often by draws and most bluffs get called. It seems to be pure mathematics in play, no real skill set required. Without the ability to force people out of draws or to really bluff how do you make money at limit if most people are fairly knowledgeable? What is your edge? Is it easier to force people off draws if the limits are higher?