Originally Posted by
Viena
The problem in here being, that they cannot expand their main two bottlenecks without some re-engineering of how their server infrastructure works.
In your analogy, it would be SE having the ability of easily adding and opening new cashier lanes (world servers and instance servers), but people having difficulty getting to them because of how the store's corridors are organized (login and instance arbiters). They cannot make the problem better without changing their corridor structure first.