Actually, it's for 2 reasons.
1. Canon started out in a garage making consumer cameras using Nikon equipment. They started at the low end and worked their way up. Nikon, before being a camera manufacturer, was a military company that made targeting reticles and such for war machines. After Pearl Harbour when Japan lost WW2, they had to find another industry and moved to camera making. Because of their background, they focused on making high quality professional equipment.
Nikon was expensive and pro-only, so the masses went for Canon consumer products, cheap and entry-level. This built a large support base for Canon.
2. Over the years, Nikon worked their way downwards from Pro while Canon worked their way upwards from Consumer. Around the 1980s, Canon brought out a pro camera that had much faster auto-focus than Nikon cameras. Pro photographers who shot sports ditched Nikon and moved over to Canon in hordes, giving Canon the edge they were looking for in the Pro market. Nikon couldn't compete against the fast auto-focus and it took them several decades to get up to par. They never quite entirely recovered from that.
Their consumer products were (and still are) a little more expensive than Canon, despite Canon being made in Japan and Taiwan (higher cost and quality) while Nikon outsources to China and Thailand extensively (cheaper, lower quality). This also makes more people (such as new buyers) gravitate towards Canon, and we all know how once you're in a specific ecosystem, it is expensive and hard to switch over.
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ALSO: To fvdbergh, thanks for the table. I think this is already more along the lines of what we were looking for. Obviously those rankings could change completely depending on what factors you were using for the comparison.
Price would probably be the foremost I would use, then general functionality. First-time buyers are going to be most concerned about what they can afford