The price recently has been more than double that of 120. I did get a 220 insert for my M645 Pro (my Yashicamat 124 can, of course, use it) mainly because I got a bunch of 220 film including Agfa Optima 400 and, yay, nine rolls of Astia I still have, in a box o' film purchase. I've shot a couple of rolls of the Optima and it was fine (cold stored, supposedly - whatever, it's fine.) I think I paid $17 for the 220 insert from KEH so it was worth it just to shoot that film.
But it really doesn't have much appeal for me. 15 shots in my M645 or 12 in my Yashica are just about ideal. 30 is too many, or would be without the interchangeable backs. I can imagine times I might like 24 shots in the Yashica, especially since it's slower to load than a 645 insert (or swapping backs.) But it just isn't a big deal. Those shooting 6x7 or, more so, 6x9 cameras would have more use for it of course.
I suspect the biggest use for it was probably wedding shooters. Since so few weddings are shot on film now, and the few that are most likely are shot with cameras with quickly interchanged backs, I too am surprised it lasted this long.