You have no control over what the buyer would do with it. They might decide to slurp up all of the user financial data flowing through the server, for example.

You have no control over what the buyer would do with it. They might decide to slurp up all of the user financial data flowing through the server, for example. Or they might leak the data due to incompetence. Even in the best of circumstances, the buyer would probably have a plan for increasing revenue, which might mean raising prices, introducing ads, or any number of things that James might not like. Finally, it sounds like he wants to continue working on the product, just at his own pace, and without the stress of running a business. This would not be an option if he sold.