Thanks for the very good question. You made a valid point that there is no way to trade your Steem and SBD now as a crypto beginner (since most of u are trading on polo and bittrex). But there are many ways around to solve that problem (by trading at OpenLedger https://coinmarketcap.com/exchanges/openledger/ or other exchanges beside Polo/Bittrex). Anyway if u are a long-term believer in the platform, u don't have to cash out so soon. There will be more exchanges coming which probably supports Steem so u have more choices in the future.