They do it with rated matchmaking. Which is not compatible with the reward scheme in Classic. It’s just that simple.
Imagine facing the top of the rated ladder in any of the MOBAs, when you yourself as a “casual player” only play near the bottom of the rated ladder.
This is the difference between the highly random matchmaking of Classic, where everyone can be any kind of skill level, compared to moba games, where they get sorted into their own rating ranges based on how good they are.
Essentially, it keeps the “good” away from the “bad”. So “bad” only faces “bad”, while “good” only faces “good”.
Which the reward schemes in those games are designed for. While Classic’s reward scheme is not.
Classic’s reward scheme is designed for the way it is now, with a mish-mash of premades vs. pugs, and pugs vs. pugs, and everyone can be any kind of skill level facing any kind of skill level.
To mess with the matchmaking messes with the reward scheme, like for example how with xrealm you’ve got games running 24/7 with queue times that’s wildly different from what it was like in Vanilla.
Don’t get me wrong, the way queues times are decided isn’t really decided by the amount of people per se. It’s decided by even numbers on both factions queuing at the same time, and if it’s uneven then it affects the queue times making it faster for one while it becomes slower for the other.
This gigantic xrealm however makes it so it’s less volatile, and makes it so you can always get a match at any time of the day or night, while with Vanilla realm sizes and faction splits being uneven on many servers without xrealm matchmaking, it depended a lot on what faction you were and at what time of the day you were queuing as well as what BG you were queuing for (some having it so bad that queue times were “Unavailable” and you could get a random queue pop several hours after having entered the queue.
Anyhoo, so to mess with the matchmaking in any way changes the frequency of entering the BG, and that in turn messes with the pace of collecting the rewards from the BG which in turn affects how many people acquires the larger rewards like reputation items and when they acquire it. It also changes how much you need to play to place in specific brackets in the ladder and so on.
In fact, if you create an “easy queue” (the solo queue) and a “difficult queue” (the premade queue) this has immense repercussions on the reward scheme as a whole. Where people get the same rewards (reputation items), despite having had inherently very different challenges in order to get them. Which in turn affects popularity of the different queues.
Which is why you need to reduce the rewards in the “easy queue” to the point of meaningless, like they did with skirmish arenas vs. rated arenas, or unrated BGs vs. rated BGs, or you just simply remove the option to queue as anything less than a full premade.
You’d still get those inherently “unfair” matchups due to there being no rated matchmaking to separate the bad from the good, but the argument that it’s unfair because it’s pug vs. premade would at least disappear.
The key difference here being that everyone is subjected to the same conditions of matchmaking, so nobody gets an “easy queue” for the same rewards while others suffers through a “hard queue” to get the same stuff.
You can’t have it both ways with just honor being higher for the “hard queue” either, that just negatively impacts the worth of the rep items while making it harder to find ppl to create premades with.
Overall, this follows a game design philosophy that rewards you the more you’re willing to dedicate yourself. This is why people have always said that this reward scheme in Vanilla (and now Classic) never rewarded skill, it only rewarded time.
Which is the whole purpose of the matchmaking as it is today. Except due to the negative social impact of xrealm matchmaking and the way it impacts the underlying motivations to work together, to turn the matchmaking so everyone can only queue up with people from the same server as full premades would help alleviate some of the negative effects the xrealm stuff has.