Even if it were currently profitable (after transaction fees), it may be more profitable to release it as a way to introduce new customers to a particular exchange (i.e. Poloniex). I'm not assuming this took place, but if the developer wanted maximum yield, working out some sort of incentive plan:

Flat free to release with "Built to work with Poloniex". Similar to "Click to deploy to Heroku" buttons.

Affiliate link /discount code to track conversions or reward accordingly