As someone pointed out (elsewhere), Nikon came out with the Z9 (gripped body) then two years later came out with the Z8 (essentially the same camera as the Z9 but without the integrated grip). Sony doesn't offer an integrated grip body. When Fuji updated the very nice GFX-100 to the MkII version, they eliminated the integrated grip.
Taken together, the upshot seems to be that none of the major manufacturers see a strong market for a high MP, integrated grip body. It's fine for people to want that, and like you I certainly 'get it'. But what I don't get is when people claim that their desire is representative of a large enough market segment to matter, or that Canon is somehow not meeting the needs of 'professionals' in general by not offering such a body. It seems like an unreasonable expectation for Canon to meet everyone's personal needs.
There's also a reason that the R5II is generally very close in specs to the R1, namely to meet the needs of those wanting pro-level performance with a higher MP count.