It has nothing to do with the feel of the faction. There are many on the horde who miss alliance dearly for its feel and lore.
The reason behind the problems is a social dynamic called urbanisation. People will constantly move to more populated areas unless there is a cost, either through environment or literally cost, that people will not put up with.
For the longest time Blizzard has done everything in their power to reduce the inconveniences associated with urbanising, and the consequences have finally caught up with them.
It starts early with servers where there are two factions but it clearly advantageous to be in the bigger faction in terms of the economy and lack of ganking and is easier to get groups.
There is no disadvantage because the queue size is independent of faction, thus the best possible situation is to be on an as imbalanced server as possible, so that’s what happens.
Some problems did eventually crop up - hard to find BG opponents for instance, but Blizzard made short work of these inconveniences by introducing mercenary mode and they even gave them the faction bonus! This was subsequently changed, but still.
Other disadvantages of being on an overpopulated or imbalanced realm, such as lack of player enemies to complete world PvP quests, were removed through CRZ.
Blizzard seems to actively encourage everyone to hop to the same realm by making sure that there are never queues even under extreme strain due to the release of an expansion pack for instance, by using phasing and truly MASSIVE realm caps.
Traditional disadvantages such as noise levels, light pollution, ooze and other pollution, and so much more simply do not exist. Blizzard are doing nothing to prevent this urbanisation, and they are also doing nothing to close down the tiny abandoned communities that are left behind, but instead simply abandon them and expect them to pay thousands upon thousands of euros to fix it themselves.
It’s dirty, it’s incompetent, and it massively degrades the experience for hundreds of thousands of players and Blizzard simply do not care. Now the problem has gone from merely a realm problem to a faction problem as they don’t do something.
It has nothing to do with the fantasy of alliance. It’s a failure if game design. There are many fixes possible, but at this point they’re going to be a little painful. It’s really bad that this happened.