Open source doesn't mean free.

> On the other hand, Steam et al are app stores where developers can get paid.

Yes, this is exactly my point. App stores have a reason to exist. They provide discoverability and a streamlined way to monetise your app, something that is sorely lacking in open source projects. A case in point for example is Krita, which is published as a paid app on the Microsoft Store. The revenue generated by the sales goes to fund the development of the project. Linux needs an equivalent.