I don't QT either. But maybe that's just because in 10 years, I've never had any fish get sick enough to justify the hassle of quarantining from the start. Perhaps I'd be singing a different tune if all my fish were wiped out by a disease. But, you don't hear about that happening all that often anyways.
If you look at it realistically, most people that join this forum already have a fish (or many) in their tank. I think the proportion that join before having set up a tank is much much smaller than those that join after they have set up a tank. So for the vast majority of people here, advising to quarantine new fish would be pointless. They already have fish (and thus could have any possible disease) in their tank. For quarantining to be effective, you have to do it for every single fish before adding them to the tank. It doesn't help anyone that already has fish in their setup.