For people who like a very upright riding position and want a lot of rise without a lot of reach, I wonder if there's some potential weight savings to threaded. Just the quill stem has to extend very long above the headset in that case. Basically a single pipe.

With threadless, both the steerer (or worse, the steerer plus steerer extension) have to extend very long above the headset, but then also the spacers surrounding those have to proceed all the way up from the headset to where the bottom of the stem is clamped. So a double pipe.