There is actually every incentive for labs to let you use their subscription in other products
Here's the thing: the alternative is not that OpenAI sells Astra at 20x the cost via API pricing, but that others make do with Luna, Kimi and GLM which are 90% as good for most things
So in the first case OpenAI gets $200/month, or even $500/month now. And in the 2nd case they might get nothing