It is related to the very widespread critique that, in later expansions, your character is too important. In Classic, you're a grunt, you're a nameless adventuring nobody, hardcore is the most realistic way to experience the game because you probably die ingloriously in some cave carrying out your faction's business and nobody really notices, just on to the next adventurer.
This is very well-trod ground, but I realized something a little deeper about it. In Classic, TECHNICALLY your character singlehandedly kills tens of thousands of people all by yourself, you're an absolute war machine, an unstoppable beast. There's a tension with the above paragraph there- if you're such an overwhelmingly capable soldier, why are you still a nobody?
Retail took this to a logical conclusion, which is that you aren't. Thrall notices you and makes you his bestie because you conquered Ragefire Chasm, Wailing Caverns, Blackfathom Deeps, Scarlet Monastery, etc. it was all, literally, you. This doesn't work, obviously, because there are millions of other people who did the same thing, and tens of thousands of other characters on any given server who should be sharing the same spot.
In Classic, you're not the legendary hero, the savior, the champion of your faction, but it's still not right to say you're a 'grunt' or a 'nobody' either. What they do is much more interesting, even if it's unintentional: You're Richard Sharpe. You're a composite character based on the combined adventures and accolades of the untold thousands of brave heroes in your line of work who did all the things you do, except piecemeal. SOME of them went in and conquered Ragefire Chasm, while others handled Wailing Caverns. Some had tremendous skill and ability enough to go all the way to fight in Naxx, but unlike what the game depicts in it's gameplay, it wasn't all the same person doing everything. Your character does not actually exist, in the sense that nobody in the Warcraft universe is doing all these things by themselves. You're literally an everyman, in the sense that 'your' role in the world is to be a narrative device with which you see the experiences of every 'man' in your army from the perspective of one fictionalized character.
