I'm sure they could also negotiate a similar deal with OpenAI but in my outsider experience it seems that negotiations around these kind of corporate contracts takes forever and when the selling point is "they're broadly pretty similar" I suspect the motivation isn't there.
“Our competitive advantage is that we believe them,” I’ve read—wonder if that’s still a [prevailing] sentiment.
(Edit - context was probably using SotA models instead of being limited to local open source only)