They already do - Canon EOM-M and Nikon J(?). They have a different native lens mount but adapters are available for legacy glass. I think they reviewed poorly

They already do - Canon EOM-M and Nikon J(?). They have a different native lens mount but adapters are available for legacy glass. I think they reviewed poorly against more dedicated mirrorless manufacturers. Reminds me of the Porsche Boxster/Cayman. Mid-engined cars is a fundamentally better design than the rear engined 911 but the company culture and legacy requires that the best performing Porsche models are the 911s. I'd love to see Canon/Nikon build a 918 equivalent, just go all out building a mirrorless using their best tech. Unfortunately they are ceding the ground to Sony/Fuji/Olympus...