The E-mount and Micro Four Thirds were already open mounts they could have taken advantage of, or gone the Pentax route and introduced a mirrorless based on their existing lens mount. The MFT mount has so many lenses because several manufacturers got together on it. Nikon and Canon could have joined up with Sony on the E-mount to do something similar, or got on the MFT band wagon.
What's more is that both of their mirrorless offerings are crippled and seem to make very little sense.It's like they were afraid to make them good and compete with their own DSLRs.
>>> Why did Canon and Nikon introduce new lens mounts for their mirrorless cameras?