Unlike all the subjective opinions spewed across the internet and elsewhere, yours and mine included, it is an objective fact that more people have decided that Canon dSLRs and lenses are the best, for them…and have done so consistently for >10 years.
The only fact is the sales number, the reason (best for them) is speculation on your part unless you mean that whatever people buys is always the best for them at that moment, but in that case I smell a petitio principii.
You don’t have to universally define “best” to understand that “best selling” is not equal to “best product” in the same way that “best dynamic range” is not equal to “best product”.
We buy what we buy for a whole bunch of reasons. Wants, needs, budget, knowledge (or the lack of it), ego, status, indoctrination, propaganda, reviews, expectations, dreams, beliefs, even facts sometimes.
Excluding the small number of people extorted or otherwise coerced to purchase a 'luxury' product not of their choosing, I'd say it's a pretty reasonably assumption that people but what they believe is best for them at that moment. All of the factors you list, and the myriad of unmentioned factors, are consistent with that assumption.
You're right that the only real facts are that Canon has led the dSLR market for the past 10 years, and has sold more dSLRs and lenses than their competitors during that period. Latin logic aside, I'm sure there are reasons for their success.
But the reality is that product sales is influenced heavily by marketing, including sponsorships, product placements and market presence (i.e. white lenses at sporting events), not by objective comparisons. Most people buy most products based on perceived and "marketed" value, and are rarely well informed about the products they purchase. I would also argue that while some might believe that this isn't true for high end pro camera buyers, that in fact it is those same product placements, white lenses at games and sponsored "big name" photographers that do in fact significantly influence camera purchases. It is very hard to not be influenced by branding and marketing.
In fact, I can't think of many (any?) companies that sell the most of anything that is also considered by "objective informed consumers" to make the "best" of that product. Maybe Canon is an exception? I have no doubt many Canon owners would like to think so.
Canon makes wonderful products that no doubt are the "best" for many well informed users. But one of the problems with being the biggest company is the need to make products that will appeal to the broadest base of users in order to maintain that sales volume, and that often translates to an apparent reluctance to introduce significantly innovative new products, perhaps partly because the bigger they are they less they feel compelled to do so.