I believe that Canon has too much invested in their current technology and is thus unwilling to discard that investment, even though much of it has been made defunct.
For example their IS system. Lens-based IS was the only option in the days of film cameras. Canon invested heavily in research and then digital arrived. IMHO, sensor-based stabilisation is much better, especially for video as proven by Olympus's IBIS. Yet for Canon their research must have a return on investment (RoI), so they now bring basically every lens out with IS, irrespective of whether it needs it or not, e.g. the new 24mm, 28mm and 35mm lenses.
The same can be said of their focus-system (the one in the base of the camera, not the on-chip implementation). A relic from heavy investment during the film days, which Canon will continue using (with the required mirror) until such time as the research has paid for itself.
It took guts in 1987 to drop the FD system in favour of the unproven EF system and it was a make-or-break decision. Canon, IMHO, must now again make such a decision and take the loss on all that "old" technology that is basically keeping them back. Mirrorless is, with regards to the entry- and mid-level segment, the future.
But the joke is that Canon need not change the EOS/EF/EF-S system in any way. Nothing in the laws of physics dictate that mirrorless must be small and with a miniscule flange distance. Keep the size of the cameras, keep the current flange distance ... just make the dang things mirrorless.