It’s a key question, actually. Unless it’s a project sustained through grants, donations, and the good graces of the developers, lack of a viable business model and sources of revenue should concern users.

As the saying goes, if the product is free, you are the product.

Specific to #nostr, while it’s still early, a number of revenue streams are emerging, from paid apps, to subscription relays, and the like. It remains to be seen if advertising will be among the ways, but I wouldn’t be surprised to see it in time.