In central/southern Ontario, nearly all homes have brick facades (stick-built frames), even cheap subdivision homes and new construction. I'd put it at something like 80%-90%. I have no idea why brick is so popular here, but that's a lot of bricks.

Brick exteriors do not burn. Brick exteriors are much more rugged to the elements. Brick exteriors do not require maintenance of painting, etc. Brick exterior houses are cheaper to insure. There's lots of reasons for brick exterior than just aesthetics.

I agree with everything you said (particularly the no maintenance part), but I think there must be another explanation as to why brick facades are so prevalent on southern Ontario houses. Other areas with similar climates and population levels (say, Minnesota) have much fewer brick homes.

It probably comes down to tradition. In the old parts of any city, all of the 100 year-old houses have brick exteriors, as well as most of the houses built since then.

Thermal mass too, I think - though it's also not uncommon to see a lot of brick construction in areas where timber is in shorter supply (whether that's because it's already been logged, is protected from logging, or trees just aren't very big).