They say (a claim that is not confirmed):
some one says M mount discontinued
M43 sensor is no good. (proof is in death of Olympus Camera Division).
APS-C sensor is good because it is a bridge to Full Frame when the mount is the same. (for Sony E, Nikon Z and Canon RF).
About the M mount...
See this.
Canon discontinues another M mount camera
Canon discontinue last remaining M mount camera - in Japan
These are the cash cows for Canon. They bring home the bacon.
Canon takes a big risk to discontinue them.
It requires courage to kill your current cash cow.
But in the long run, it is expected that Canon wishes to consolidate their camera bodies under 1 RF mount.
Just like what Sony E mount and Nikon Z mount will do.
Then you ask, why did Canon introduce M mount in 2012?
Perhaps the answer is that in 2012, Canon did not anticipate that they would make full frame digital mirrorless ILC (which they did later on in 2018).
Or maybe the RF mount was not yet fully developed in the year 2012.
Hopefully Canon will be able to make suitable camera bodies and a range of smaller RF-S lenses and convince consumers to buy them.
Hence the R50, R10 and R7.