They get paid in Steem which is generated every day. It does not come out of the market cap money, it is generated like any other cryptocurrency.

The Steem network continually creates digital tokens to reward content creators and curators. Some of the newly-created tokens are transferred to users who add value to Steemit by posting commenting and voting on other people's posts. The remainder is distributed to holders of STEEM Power and the witnesses that power the blockchain.

You can read more about it here: https://www.steemithelp.net/#/new-page-3/

and here: https://steemit.com/faq.html