Treks of that era, like Raliegh in their heyday, may have had some quality control issues as their US handbulit operation started to get over run by demand. But that is rather exceptional in my opinion. Generally speaking, the late 70s and early 80s US made Treks are wonderfully made bikes. Some of the best frame makers like Mike Appel got their start there.

Me? I'm guessing that steed got rode into the ground while being fully loaded.

The 720s of that era with their combination of thin walled 531 (relative to 022 and 501) and super long chainstays were known for bad sway and stability problems. Just too much distance for such light tubing.

My guess is that bike got ridden:
a) by a heavy rider
b) on rough roads or worse
c) with heavy loads on a rear rack
d) all of the above

They are really quite unique bikes, especially in the non-canti versions. I can't think of another bike with those 47cm stays.