My suspicion is that it's a way to break into more developer workflows for Grok, even if the market share is relatively small. I've never used grok and don't plan to at this point, but I have highly respected friends who say it is pretty damn good, and some of them even started using Cursor because of this pairing, so anecdatally at least it does seem to be working.
I've now switched to Grok 4.6, I was previously using Opus 4.8 but Grok is good enough now, and way cheaper which is the important part.