PB
Addicted to ArboristSite
+1 Absolutely right Phil,
Maybe Plant Bio or someone can say why this happens? It may be human impact or just certain weather conditions, that allow a bug infestation too get out of control, but that's what happens and they are only trying to slow it down by limiting the movement of wood in infected areas.
Here's in Maine we have/had Tameracks (hatmatack) Eastern Larch that was once the king of ship building lumber. The stuff lasted forever underwater and even exposed was pretty good. The Larch Beetle put an end too the commercial viability of that tree. Still too this day their greying skeletons can still be seen standing in boggy areas, as a testiment too the durability of the species. They are starting to make a comeback and I for one hope they do. It's an excellent tree with a long history of medicinal, and commercial uses.
I am not an entomologist, but I will take a stab at it. You can think of it as population control. If you were confined to a small area with limited resources and unable to move freely about, would you have 10 kids? Kind of the same with the EAB. If it is localized it controls itself in a way, albeit not good by any means but it spreads much slower. If you take these insects to fresh wood, they multiply like rabbits until they are saturated again. This goes on and on. If I remember correctly the EAB is not native and has been introduced from a different continent from infected wood. The same principle that Mantis was complaining about, freedom. Some country didn't want to take away someone's "freedom" and stop the spread of the bug now we have it here.
The weather does also help with insect control in general. A cold winter will usually kill off a large portion of the insects, but with global warming this is having less of an effect each year. Look at the pine forests of Alaska for an example of this.
Again, i am not an entomolgist, just general ecology.