A torsion spring is great because as it unwinds, the tension decreases. As the garage door transitions from 200 lbs of vertical load in the closed position to almost 0 lbs when it's mostly parallel to the ceiling, a properly sized and wound spring reduces the force in synchrony with the door position.
Wouldn't a counterweight provide insufficient force at the bottom and/or excess force at the top?
But they require space and a sturdy housing. Springs are as compact as you can get.
There are also some safety concerns, a cable connecting the door to the counterweight can break, and/or slip. This can result in pieces of metal flying everywhere. A broken spring typically stays contained.
Personally, I would do one of the counterweight systems for my new house.
Not so for a 100%, 50%, and 0% open garage door. The 0% open door is the full weight; the 100% open door has very little weight (as most of the door is on the horizontal track).