Canon has primarily survived off brand loyalty with professional photographers driven by the extremely high quality lenses they produce. This too has been challenged lately by Sony and their partnership with Zeiss, meaning Sony lenses for mirrorless are on par or in excess of the quality level you can get from Canon lenses and Zeiss is financially able to offer similarly high quality lenses to the wider market, cannibalizing first-party sales. Nikon has historically had worse lenses than Canon and this hasn't changed significantly, but they've made huge leaps in R&D for large telephotos with usable fresnel lenses at 300mm and 500mm focal length.
Canon had some opportunities to right the ship, but their management seems incompetent. It's sad to me that they're in this situation because I respect what they've done for photography for decades. I don't see this improving though.