It probably doesn't matter from a technical angle, but I speculate that Microsoft didn't properly acquire OpenAI because the former was concerned about reputational risk should ChatGPT or some other cutting-edge AI mass-product blow up in some way (and the awkward optics of "Open"AI becoming a M$ IP).

And it's pretty clear (from their own words) that regard for that risk held Google back in aggressively releasing such products.

Now that this phase is over, I expect MS to fully acquire OpenAI to better signal that they are committed to full-spectrum AI products, as Google is doing this week.