Part of the reason you could not do this on BTC is the transfer times and cost. It's take BTC at least 6 mins to validate a transaction, here is takes 3 secs. Running this platform on BTC would be like using carrier pigeons for it's post. Second it is free to send transactions on here. The amount of Steem Power you have determines how often you can transact. The cost for just posting BTC at these rates would be huge for the user.