I'm not surprised, having seen what drives automotive assembly. Here's a hypothesis at least:

Trek in those days was still a bunch of bike guys transitioning to mass production. One big issue is to have the right parts at the right time. If one item is missing the line can stop, even if it's a small group of framebuilders. If they ran out of (for example) English BBs and the buyer could get a small run of Italian-thread BBs, why not go for it? It can be a better solution than stopping the line, changing over to a different model, then changing back to 720s when the supply is better.

BTW, my 1984 610 originally had 27 x 1 1/8 wheels. I converted to 700c many years ago. Right now it has Mavic MA-40 rims, 28mm Conti Gatorskins, and 35 mm SKS mudguards. No clearance issues. Has toe overlap, but no tire-related clearance. The fenderline is not bad, either! I get away with the original Shimano 6207 medium reach calipers, with the shoes at their end of travel.