The War Asset list only shows what each race has contributed to your personal war effort, which is to complete the Crucible and reclaim Earth. The rest of the turian force is bogged down on Palaven and policing/evacuating the rest of the galaxy. RShepard227 (talk)
- And from the news we get from Palaven, the fighting there isn't going great for the Turians. As for Geth, Quarians and Krogans the Reaper forces still haven't dealt them a serious blow like they have to, let's say, the Asari or the Alliance. JohnMD (talk)
Much of their military is tied down fighting for Palaven
Also, as stated throughout the game with ongoing conversations with Garrus onboard the Normandy, the Turian Fleets were getting decimated by the Reapers. Hackett had sacrificed the 2nd Fleet so the rest of the Alliance fleets could escape, that is why the Alliance is the strongest. The Asari and Salarians withdrew to their own space in a futile defense of their homeworlds and neither one of them were really strong in numbers of forces.
Turians are also busy taking care of the other races. Over the course of the game you hear that they also sent forces to protect the volus and elcor homeworlds. They're the king daddies of galactic defense, so it makes sense they're the ones who are most tied down during the war.