There may be a few things at play:
*Ideally, those trees are planted at the correct depth, even in the tree pits.
*there are systems that allow for successful rooting under sidewalks (Silva cells, for example).
*Many urban trees are living about 7-13 years before replacement, so often things are not done correctly, and the trees don't make it.
IF the tree was planted in your "well" at the correct depth, AND there was a way for the roots to get under it and out into the yard (which I assume that second part is the case since you said it was put in after the tree...), then it may make it for the long haul. However, we see deep planted trees dropping off in their "teen years". So, 10 isn't unrealistic to expect. It isn't hard to keep a tree limping along for 10 years. As they age, they need more resources. Or, more likely, for deep planted trees, that is when the trunk is really trying to expand but is girdled by encircling roots.