Comment by koreth1

This is maybe not in the spirit of OP's question, but I do it by having successfully made the case early in my company's lifetime that we should open-source most of our code.

Nearly every piece of code I write at work is part of one of those public, Apache-licensed code bases. Which means I spend most of my time working on OSS.

Are these projects the kind of thing anyone else will ever use? Probably not, so long as the company stays in business. The business case my team made was focused on transparency and long-term viability: our customers can see exactly what we're doing with their data and how our systems work, and if we go under, they have a realistic way to continue using our software. This hasn't ended up being a huge selling point, but customers have definitely mentioned it as one of the things they liked about us.