To me, at the moment, the issue is not Canon continuing to make great DSLRs (although I'll come back to that one), it's that there is no serious mirrorless option from Canon for those who do wish to move to mirrorless for whatever reason. At the moment, it's an all or nothing choice; if you want a serious mirrorless solution, by definition, you are forced away from Canon into a competitor's arms. Why not simply have the choice of the two within Canon's ecosystem? Very clearly there are users who want either or both, so I believe Canon's fear of 'cannibalising' DSRL sales is unfounded. However, if that belief does have foundation, it is even more pressing for Canon to produce a very serious mirrorless offering, as that would mean that, increasingly, they will simply lose those increasing mirrorless sales to their competitors.
That said, what really, genuinely, suprises me more is that even within DSLR systems Canon severely lacks innovation in some areas. This is where they are market leaders, yet there are competitors who even now are building more modern, innovative systems. E.g. the Pentax K-1 (or MKII) now that Pentax's lens lineup for modern full frame sensors is fleshing out. For stills, at least, if I were buying into a new system, I would be very seriously looking at a K-1. IBIS (including hand-held pixel-shift hi res mode on the mkii, and auto-levelling, and AA-filter mimicking), great image quality, fully articulating LCD, astro-tracing, and a logic board upgrade for owners of the mki to upgrade to mkii!. All this at around $600 less than a 5D Mark IV.
So, Canon have the size and robustness of a DSLR body to play with, to which any of these new, innovative features could physically be added, they have more patents than any other company (we're constantly reminded), yet a lowly competitor just put a ton more innovation in their DSLR. That to me is an even bigger issue than the lack of a pro mirrorless at this point; if Canon are going to specialise in DSLR, they could at least bring their high-end offerings into the 21st Century and justify that decision to stay away from mirrorless.