It sounds logical that you hit the nail on the head with this assumption.
I hae the R5 and the first thing (after the EF-RF adapter) that I got was the battery grip. It double the battery life on one hand and allow you to each even more short with low battery level than a single one. So I wonder why they discontonued it for it also match the R6II which has some long shelf life a head of them.
It does seem odd, but perhaps not surprising. After all, Canon did not even provide a battery grip option for the R7. I suspect that means grips aren’t very popular with the broader market (which we here don’t represent), or at least Canon grips aren’t very popular given the much cheaper 3rd party offerings.
I also found the BG-R10 not very comfortable to hold. The grip for my 7D feels a lot better, but my 1D still feels the best of all. I've used grips on all my DSLRs, including a 3rd party one of the 100D/SL1, but I don't plan on getting one for the R5II. The extra height gets in the way when I try to photograph solitary bees and jumping spiders, unless I shoot upside-down. And that isn't an option when using a flash.
I far prefer the integrated grip. I, too, used grips on all my DSLRs, the T1i/500D, 7D and 5DII, before getting the 1D X. I'm ok without one for a travel camera, and the R8 works for that nicely. But for that use case, I'm not handholding the camera for long periods, it comes out for a picture then goes back in the bag, or it's on a tripod. For my everyday camera, I will be sticking with the 1-series body style. The integrated grip is more comfortable to hold, and the controls are typically positioned much better than with the accessory type, and there's no play in the connection that can lead to vibration when on a tripod.
I would not expect a new grip for the R6II, more likely Canon has sufficient stock of the current one that they have no need for further production.
After years of using accessory grips, I switched to the 1D X. The reasons you list are the reasons I likely will not go back.
