From the Whitepaper: "The purpose of liquid STEEM is to facilitate changes in ownership between long-term holders. It is this change in ownership that the network 'taxes' to fund growth."

Wealth transfers result from content creation, curation, mining, and liquidity rewards. It's fascinating that this creative mechanism replaces and is equivalent to Bitcoin or credit card transfer fees... but has a covert quality that is much more user friendly. Steemit appears to be "free", but, of course, nothing is free.