Why is tracy mcgrady so washed up?

Why this guy so not good anymore.. I know he's been through injuries and surgeries and things.. but they way he was so skilled a while back there is absolutely no reason he should be playing like a 49 year old at age 31.. 31 !!! i mean I know 39 year old's that can dunk like they were teenagers and theyve had surgeries all over the place.. any opinions ?