I love Thor’s description of comparing retail to (hardcore) Classic:
Retail is a power fantasy whereas (hardcore) Classic is a D&D session.
The long and short of it is that when a game gets “solved” then a lot of it becomes boring to people. In Retail you have to push beyond the power fantasy levels but in a world where you are dealing with power fantasies at those levels, it means encountering enemies where “one mistake, you dead” sitatutions. Most people are fine with that because power fantasies are fun.
Hardcore classic isn’t solved because if you make enough mistakes or just one egregious one, you dead, and you gotta start over. Besides Season of Discovery (do note the name though, as that’s a pretty big clue as to why that one works), Classic doesn’t have that. The thing people “discover” when going into Classic is simply that the game was different, and it takes finding what’s unsolved in order for Classic to be anything other than a really, REALLY slow running simulator.
So in short, retail is a MMO and the premise of it not feeling like one is beyond belief silly at best.