Craft CMS follows an interesting business model: a self-host product which is purchased with the source code of the product i.e. 'source only'. It's not open-source - the source code of the product cannot be shared or distributed by others, but it can be modified by the customer to suit their needs.

The source code is published on GitHub so anyone can see it. Presumably the product creators trust customers will pay for the product (if some do not, it probably doesn't matter to profitability). Another profitable PHP product called 'Kirby CMS' also follows this model.

The idea of 'source only' is not new at all. Back in the late 90s when Delphi was popular, many developers created and sold components to other developers (e.g. UI widgets). These components came with full source code of the components but they were not open source.

The label 'source only' is considered a dirty word among some open source advocates. But if you are building a B2B (Business-to-Business) software product, 'source only' is a viable option to successfully make a living from your product - one that isn't completely closed source.

(As an aside, here's the Craft CMS licence: https://github.com/craftcms/cms/blob/develop/LICENSE.md)