It is natural for the brands that dominate with one technology to be slower than others in adopting a new alternative: in the early days when a new option allows an "insurgent" to take sales from incumbents, the incumbents will initially see it mainly poaching sales from their own existing product lines. But they can also afford to enter later and catch up, if they have enough ability to leverage existing advantages (lenses, technology that carries over, brand goodwill, market presence, financial resources, etc.), and can benefit from letting the insurgents try various approaches and make some mistakes, and then step in when the best approach is clearer, the new technology is more mature, and its advantages are more widely recognized. I doubt that Canon and Nikon have both mis-timed their entries to the "serious EVF camera" market.
P. S. EVFs and focus-by-wire are not tied together; there have been FBW lenses for SLRs (including many for Four Thirds DSLRs), and direct manual focus coupling in some lenses for EVF cameras. Some high-end Olympus MFT lenses allow switching between both options.
