This area sits in a cold, severe climate band, and cold is hard on wound steel. A torsion spring loses a little tension every winter as the metal contracts and expands through freeze-thaw cycles, and by year twenty or thirty that fatigue catches up with it - usually on the coldest morning of the year, which is also when you most need the door to open.
Because Ontario's housing stock is newer than most of the service area - median build year 1983 against roughly 1957 across the wider county - most of the springs failing here now are original hardware finally reaching the end of a normal life, not springs that were already old and neglected when the house last changed hands. That's a different failure pattern than what we see on the older stock closer to Mansfield, where springs have often already been replaced once or twice. It doesn't make the break less sudden - a spring gives out the same way regardless of the house's age - but it does mean the fix is usually a straight swap rather than untangling decades of mismatched repairs.