Apparently you’re unaware of the big blue post discussing megaservers and the problems therein.
From [Classic] The unacceptable state of Classic servers - Community / WoW Community Council - World of Warcraft Forums (blizzard.com):
Relevant section quoted here for convenience:
The Mega-Realms in US and EU are full (also; Layers are not the solution)
We’ll start with the easiest and most clearcut statement to make. The mega-realms in US and EU that are queuing are completely full. This statement is the absolute state of things, and there is no additional capacity we can add to these realms to allow more players on, or to reduce queues.
One common suggestion we get is to “just add more layers”, and it’s very important to understand that layers do not add in any way to capacity. Layers are a Classic-specific solution to alleviate congestion in the game world in densely populated areas. The way they work is that when a certain threshold of players congregates in a small area in the game (say, in Blackrock Mountain) the service will spin up another entire copy of the game world to try to load-balance any new players that log in. This is to prevent a situation where large numbers of players congregating, casting spells, sending server messages and updates to one another causes a severe degradation of the entire service/game world. This functions in some contrast to the “sharding” system that modern World of Warcraft uses which basically does the same thing but spins up additional shards on a per-zone or per-area basis.
Neither of these systems increase realm capacity. Realm capacity is dictated by the total number of connections that the service itself can handle. Every time a player connects to a realm, that connection interacts with numerous services, systems, and adds to the total load on the persistent database that the entire game relies upon to fetch data related to players, spells, quests, creatures, Auctions, etc. When that total number of connections to a realm’s DB and services reaches a certain number, the service will degrade or fail on multiple levels, leading to symptoms like severe Auction House lag or outages, Chat performance degradation, or lag when attempting to loot items. Never in wow’s history had the capacity of realms been as high as they are now, and even with our modern capacity we can still sometimes experience performance degradation when the realms are full and DB load is at its peak.
So put as plainly as possible, we cannot increase capacity any more without inviting additional and likely cascading failures to the service. At present, the best and only way to resolve this issue for the impacted realms, is for people to leave the realm via free transfers. There’s no technology solution to this. There is no hardware solution to this. This situation will not improve when Wrath of the Lich King Classic launches on September 26th, it will only get worse.
Further input from Aggrend in the same thread:
I also just want to reiterate this point though; we’ve raised population caps to accommodate mega-realms to the absolute limit of current technology. I’ve seen a lot of armchair server engineers say things like “just add more hardware”, and I can’t stress it or put it any more plainly, the technology to allow more than we have on realms now does not exist. We’ve added the hardware, we’ve optimized as much as we can optimize, and the current demand on these few realms is just too much. Continuing to push our luck and find ways to reach ever higher realm caps has hit a point where we can’t go any further, and eventually something had to give. That something has given and we are going to be taking different approaches to this problem going forward.