There are several bots that constantly trade arbitrage between the internal exchange and external exchanges. When you sell on the internal exchange they will often go and resell that SBD on external exchanges and vice versa. In most cases (including this one), markets are well connected and it doesn't make much difference (if at all) which particular exchange is used.

One thing that will be necessary if and when the amounts get larger is to be smarter about how it is sold rather than just dumping it all on the market in one go. Right now that isn't an issue though, and I'll address that if and when necessary.