OpenAI is still developing their own chips with Broadcom, but they are not operational yet. So for now, they're buying GPUs from Nvidia to build up their own revenue income (to later spend it on their own chips)
By 2030, eventually many companies will be looking for alternatives to Nvidia like Cerebras or Lightmatter for both training and inference use-cases.
For example [0] Meta just acquired a chip startup for this exact reason - "An alternative to training AI systems" and "to cut infrastructure costs linked to its spending on advanced AI tools.".
[0] https://www.reuters.com/business/meta-buy-chip-startup-rivos...