What I don't understand is that something had to have changed for this to happen with this expansion specifically.

With Raubahn it could be explained by there possibly being more people playing the game than at any one time before, not to mention there being almost nothing in the game to do at all up to that point. But 4.2 and 4.3? They're just patches that shouldn't have anywhere near the volume of people on the same quest as say, 3.0. Looking at the login queues upon expansion release compared to these patches is proof enough of that. Something has to have changed, which to me says that it can be fixed, they just don't know how.