My speculation....
Canon is not stupid enough to put out a new camera with essentially the same specs as the R5, and then expect people to buy the roughly $2000 more expensive version. The R5 is meant for those wanting that "all-arounder" - the camera that does everything really well, but is not specialized. Their top of the line, integrated grip cameras are specialized cameras meant mainly for news and sports shooters. There is no reason to think that has changed. The input from that target market has clearly for many years now seems to be - keep the MPs low. Speed and convenience are far more important than high MPs which are not needed. Despite what so many gear-heads seem to think, keeping the MPs low is not being "5 years behind, or "inexcusable in 2021" or whatever similar comments are being used. Many pro photographers think 24 MP or similar is perfect or "the sweet spot" when it comes to MPs. Sony A9 II and the Nikon Z 6 II are 24 MPs and are new cameras and apparently not 5 years out of date.
What has changed, however, is that Sony, with their A1, has gone higher MPs with their flagship. Nikon's Z 9, their new flagship, is rumored to be high MPs as well. So, I think Canon has mapped out a strategy to continue to target their news and sports "series 1" users - with the R3. High speed, low MPs. And then with a "flagship" camera that is more in line with Sony and Nikon, with higher MPs, that being the upcoming R1.
Of course, I have no special insight and can be completely wrong, but I do think people in foruums almost always ignore the taget market for a product. And the target market seems to be sports shooters. So the camera will be geared for that market, not for those looking for a slightly better R5.