Steemit doesn't convert fiat to Steem or Steem Power. This needs to be done somewhere. New people joining often do not have BTC, ETH, Or Litecoin. Which still is not available to be purchased directly from Steemit but is available to be purchased from blocktrades easily and many other exchanges sell Steem. But you first still have to get the country currency converted into digital dollars.

Maybe there is a marketing reason to go through third party distributors. The ease of use and their own white paper states they are trying to help people break into crypto currency. Which it does allow people to earn some small amounts of crypto and learn about crypto. Makes it hard to buy it though for new folks.

Changelly from time to time drops Steem purchases. We are thinking about offering Steem for sale on https://SteemThat.com in the near future.