I don't doubt that all of these figure in the rationalization, but do you think any of these is actually the reason? Bicyclists, and the whole bicycle industry, have a way of deciding "what's best" and insisting on that, to the exclusion of other things. Throughout the 70's and 80's bike shop sales people routinely told racer wannabes that Campagnolo was the best equipment, not taking offerings from other manufacturers seriously; and the customer was generally willing to accept this recommendation. In that period, cantilever brakes simply were not available in the US unless one specifically sought them out and had a frame builder customize the bike. Why? Well, we were told there wasn't a market for them, which was no doubt true, but misses the point. There was no market for them because most customers didn't know about them, which was both the reason for and the result of the fact that most bike shops didn't carry them.

The real reason why road bikes don't come with cantilever brakes is as simple as this: road bikes don't come with cantilever brakes. Anyone knows that. If you want to go deeper into the question than that, you will get a bunch of rationalizations that may or may not have any validity at all.

You will see exactly the same phenomenon if you ask why road bikes don't come with internally geared hubs, or why they all have such big wheels.