yeah my assumption is you would need to be a platform like coinbase or something where the added convenience for people trading on your platform was the benefit you got from it and it just not costing much was sufficient
As you described, theyre incentivized to properly hold and maintain the reserve assets because A) They are exposed and liable to US laws (Coinbase is a public US company) B) They reap the benefits of having a native stable coin for the users on their respective platform.