Ty for the thoughtful tag.
I would suggest to you that your perception is probably skewed by some of nicest blocks, but many look more like this:
View attachment 477413'
The trees aren't particularly close together, they're small'ish and fairly young, average age of death for the trees planted in the tiny concrete boxes is about 5.
You do see exceptions to that though, even in the bad blocks:
View attachment 477422
That tree, above is at least 12, and maybe a bit older.
This one, below, is a Honey Locust, and must be decently over 20 years, possibly 30, if you see older, bigger street trees in Toronto, particularly in boxes, this is most likely species, its Toronto's 'parking lot tree', it can put up with a lot.
View attachment 477427
These trees I think will provide quality canopy in time:
View attachment 477430
Unlike much of Danforth, these aren't in tiny boxes, but in a continous soil trench with floating side walks and large planters near the surface.
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I think what you would find is that this section of Danforth has a few really good specimens, despite the tough conditions, largely because it was one of earlier streets to get street trees, and those few that survived have now had decades to grow.
That will pre-date the BIA by decades.
While I don't know this, it would not surprise me if a conscious business owner or resident saw to watering or fertilizing some of those better looking trees at one point.
Though, it could just be that they were exceptionally tough specimens.
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Tangential side note, I was walking this section of Danforth this past weekend as well; you may well have biked past me.
Next time you're on that stretch, remember to offset all the benefits of cycling everywhere by stopping in at City Bakers Collective and consume something so rich it will add twice as many calories as you burned! LOL