I was also hoping Canon would keep the EF mount but after the fact they introduced RF Mount I looked at the history of Canon and found that Canon is one of the companies that have changed SLR Lens mount very aggressively.
R Mount 1959 till 1964
FL Mount 1964 till 1971
FD Mount 1971 till 1987
EF Mount 1987 and counting
EF-S Mount 2003 and Counting
EF-M Mount 2012 and counting
RF Mount 2018 and counting
After looking at that data above I am not too surprised with Canon's decision to introduce a new mount and it makes perfect business sense because they can sell all the same FL lens again to their customers at a higher price than their EF counter parts. Something that does not makes sense to me is at this point Canon has at least 3 active mounts (EF, EF-M and RF). Obviously I am assuming EF-S is dead already. I thought Canon would kill EF-M at some point but this news says that EF-M mount cameras are number one selling cameras across the globe. So it sounds like Canon will continue with all 3 mounts and at some point they will stop producing EF lenses and RF and EF-M mount will continue as is. To me it makes sense to have a RF and a RF-S mount like EF and EF-S where people can graduate to full frame cameras and continue to use some of their RF glass but Canon obviously thinks otherwise.
To be fair though, they didn't really change the mount that much.
The R, FL and FD all used the same basic breech-lock mount/bayonet but varied in aperture control functions which also meant they didn't retain full functionality if a newer lens was used on an older body and vice versa.
EF-S is still the same old EF mount just with the rearmost lensgroups protruding into the body (so they couldn't be used on all EF-mount cameras and customers needed to know this, hence these lenses were designated EF-S).
EF-M mount was completely new as was RF.
Also, add in the M39 mount they used before R/FL/FD.
So since their beginning, Canon have introduced a new mount 5 times. Two of those were recent.
Similarly, Minolta went from M39 to SR/MC/MD (same mount, added functionality similarly to Canon R/FL/FD) to A. Then their camera business was bought by Sony and E-mount came around.
Nikon? S-mount to F-mount to Z-mount with the Nikon 1 mount as a sidekick for a while. F-mount evolved to have various F-mount generations similarly to SR/MC/MD and R/FL/FD except it had more success in doing so and also evolved into something similar to EF (with the lenses with electronically controlled aperture and built in motors being useless on vintage F-mount bodies)
In short? Canon don't stand out all that much in regards to introducing new mounts.