Every company will surely have their method or strategy of making money for the purpose of paying it's workers and using part of the earned money for the development of the companies. This is why feasibility and Viability studies is very important before setting up any business or company.
As for steemit, one of the strategy adopted by Steemit Inc is by enabling ads services on the Steemit platform whereby the company is able to earn by placing adverts on the Steemit platform. This is surely why we have lot of adverts on the Steemit website.
Another strategy adopted by Steemit Inc is by it's reward system supplied or generated by the steem blockchain. There is actually some percentage that is distributed to the Steemians when they create content, invest, upvotes, etc while some percentage are distributed to Steemit Inc.
There are the two strategies i know of for now and I hope you will find this helpful.
Thanks for reading and I hope this helps.