Aggressive much?
By "an entire expansion where you ran dungeons for rep" you mean wrath? The lfg tool only came with 3.3. before that, you had to manually look for people, on your server, which took a LOT of time. Nobody (or not many) farmed dungeons
solely for rep.
I'm also talking about doing the thing in
it's time. If you dinged on the first or second day and you wanted to max out your reps asap, you did the dailies, and wore the tabard in dungeons obviously while you farmed gear or did your daily heroic. But you didn't farm dungeons day and night, there were no groups if you didn't have friends with similar aspirations and a lot of free time. And even if YOU had a lot of free time that didn't mean your realm or battlegroup had the same free time. like I said: group finder was often empty, you could clearly see how people's work shift ended/kids got home after school. It was not like today that you can find a group for pretty much anything, anytime. Especially on a smaller or mid pop realm.
Sure, if you want to farm rep TODAY, you jsut head to the dungeons and kill stuff. But not in the first 1-2-3 months of Cata. It wasn't a thing. Players were flooding the daily areas.
Care to show me your armory? You can see mine in my sig, you can see how I progressed in my reputations. Reps are always the FIRST for me in a new expansion/patch (lol not since Legion). So i kinda know a thing or two about rep farming.
In wrath, you were lucky if you had 4-5 achievement hunter "hardcore" player on your whole realm. Achieves were new, and divided people as people started with different tasks. Before group finder, crossrealm groups, connected realms, and people playing so much less it was very hard to do group activities.