I think the implicit assumption is that you are doing the majority of the development, and you want to make money from licensing, and you want to be the only one making money from your product. So basically, the plan is to make money exactly like a proprietary software company would make money, except that you make the product open source for marketing.

I never understood why people thought that was a good idea. People like Open Source because they don't want to depend on a single vendor, and yet these companies want to be the only vendor of their Open Source solution. It doesn't make sense.

Control. If you control your IP, then the company is more valuable because there are more options (whether selling the company, relicensing/dual licensing or something else).

It's similar to developers assigning copyright when they make a contribution to an open source project--keeps control in one place, makes it easier to make long term decisions about the project (for the project's maintainers).

> If you are running a commercial business on top of your open-source solution, it is paramount that you own the product's full IP.

That sentence is even completely absurd. Suppose you ship a product/deploy a service that includes, among other things, Linux and PostgreSQL. Is it paramount that you own the full IP of Linux and PostgreSQL?...

What is paramount is that risk needs to be reduced, mitigated, transferred, avoided, or even sometimes accepted. Risk must be managed. That is why some companies want to own the OS project, and others want to pay as employees the prime contributors.