They give out loads of money if they have high traffic why would they be giving away free BTC?
i you open a faucet's page you can notice 2 things there are a lot of advertisements and if you move your mouse to the advertisements on their sites you'll notice they are from a couple of ad providers like anoymos ads, adbit, googleads, ..... the more traffic they get the better ads and more money they earn
visit this for getting the general idea:
https://adbit.co/?a=Advertise1st place is freebitco.in with 0.4 BTC/day