Here is a chart compiled from CIPA data on yearly camera production

Yearly camera production taken from CIPA data
The highlighted fields above are peak numbers for the respective column. Starting in the 2017, Canon began reporting total interchangeable lens camera (ILC) sales in their financial statements. In general, Canon has always accounted for roughly 50% of the interchangeable lens camera market.
When EF-M launched, the ILC market was quadruple what it is now. When RF launched, the ILC market was double what it is now. Canon, or any other manufacturer, can not continue to support four different mounts in an era of drastically reduced unit volume. The casual shapshot photographer that was buying DSLRs in droves a decade ago, and compact mirrorless cameras a few years later, are now mostly just using their smartphone for photography. Not only is the camera market a tiny fraction of what it was, but those still buying cameras lean much more towards the prosumer/professional end of the spectrum.