This question comes up every single time any MMO launches any expansion ever. The servers are designed to handle an average amount of traffic, and expansion launches are basically the exact opposite of that. People who demand the company just "get more servers" are basically demanding an expensive, permanent, and not-guaranteed-successful solution to what is a very temporary problem.

It's frustrating as all seven hells, but this is a case where we should just bite the bullet and wait it out.