So let's entertain that this is in fact the case: it makes no sense in practice to self host for production. Even if that is the case, you're still better off building on top of an Open Source product because you're in a much stronger position in being able to fork than hoping that the company you rely on will stay around and not charge you to death.

A lot of products we all use underwent complex business changes, but the Open Source ones still are here for us to use. MySQL had a tumultuous past and yet there is a very active version of it hanging around under a new business.

The marketing angle is for the company to leverage, but the open source nature of it is for the user.