are they wearing evenly across the tread???

if they are then your next option is to look at the wear rate number

i think the lower it is the softer the compound the quicker they wear

i presently have Arturos with a wear rate number of 400 (+ i think) and have done 30,000km and they look less that half worn, however i travel mostly freeway so little chance to go screaming around corners

back awhile the bridgestone potenzas had a reputation for wearing out quickly, a very soft tyre compound

but they stuck to the corners like glue

so first check your tyre type and softness factor that might explain it all