But you have to take into account the fact that so many people don't QT without losses. The numbers don't lie--most inexperienced people don't even know QTing exists, yet they still unknowingly buy healthy fish.
The average inexperienced hobbyist has a modest size tank, and is, on average, buying very inexpensive fish so not such a big risk for them. I couldn't afford to replace my fish if something wipes them out.
As I said it's a gamble, not important to some people, critically important to others. Guppies, mollies, platys, cories, neon tetras.....some of the most popular first fish for inexperienced hobbyists. And some of the sickest too. I can't even look in those tanks in fish stores most of the time....there's either shimmying or ick going on in most of those tanks along with starvation most of the time. Who knows how long these seemingly healthy specimans actually live in those hobbyists tanks.
I know I don't think it's fair to give a newbie an idea that it's not a gamble to not QT. They need to know there are risks involved.