I see the issue with these more as if you are paying for it, one of the decision factors to buy it might have been that you have the opportunity to go to an open source version if the relationship gets bad.

Sole source vendors are really risky, so open source gives a little control back to the buyer that the vendor won't lock them in then screw them later (oracle).

So now if you're paying for Cockroach, you're effectively on proprietary technology with no negotiating levers.