Because all I see (and this goes for every prof) is reduced cooldowns, increased damage, and bit of utility here and there. Marginal.
Now I know this is a case of YMMV, but one would expect trait choices to actually push your character into a certain direction to a significant degree, and after that you'd compliment it with gear and weapon choices -- like in pretty much every other successful MMORPG. However, it's not the case in GW2.
Let me present a modified version of the Warrior "Sonic Boon" build, which is the reason why everyone goes ape for Berserk warriors in LFG.
It provides one of the best trait-gear synergies in the game, and that being said, it's still kinda meh. Because if you take away all those traits, what do you lose?
Damage (from traits and from less might stacks), cooldown reduction, and some bleed/vulnerability. And shout healing, which is so little you barely notice it.
Okay, great. Of course I would miss those things, but it sure as hell doesn't re-define my character.
But I guess I just want more profound results from a talent system in an mmo.