Once a player sets his or her dual talent trees, do you think the player will change them? The chances are that the player will not and simply cycle between the two.
When there is a single talent tree, and a player has to switch to another specialization, that player has a choice in many ways: what talent tree? What specific talents do I want? Why do I want them? Each and every time they do a talent change. This is the benefit that is less likely to exist with the implementation of dual specialization.
I have changed my talents many times, on many characters, and rarely at all do I pick the same exact talents after the change. I may want to put 4/5 in one talent and 1 in another, and that’s not even to optimize.
Dual talents create a laziness. Once it’s set, it’s done. One for PvP and one for pve. Or one for heals and one for tank. Whatever. The laziness comes from the ease to switch to a new set of talents without consideration. It’s a short cut, but it ignores a pathway.
What if you set both talent trees up as a healer, one for PvP and one for pve, but then you want to be a dps. You’ll have to swap both. So in other ways, dual talent specialization adds twice the complexity.
Certainly players see it advantageous and that it “literally makes the game better.” But better is subjective. And often times the best choice is your own choice. Dual talents take that away from you, and you are less likely to veer into your own wants and desires after you set your dual talent specialization up, presumably by following a guide’s optimized PVP and PVE setup.
In this regard, less is more. Let’s keep it that way and look elsewhere for changes.