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the tread depth (called non-skid depth in the industry) is one of the biggest factors determining cornering stiffness of a tire. Less tread depth = stiffer with crisper cornering. The closer the steel belts are to the road, the less flex before you start turning. And, with less tread depth, you can afford to use a more hysteretic (grippier) tread compound without risk of overheating and blistering when going fast. Big meaty tread blocks without sipes also stiffen the summer performance tires vs AS.
The "racier" a tire, the lower the non-skid generally. True UUHP tires are almost always thinner for this reason (road-going "track" versions are often 6mm or less), race tires are thinner still (have you ever picked up a true race tire - light and thin, isn't is?).
Comparing an all-season to a summer tire isn't fair to either, each has a job to do. The summer will be useless in snow and even colder temperatures sometimes, the all-season lost on the track or true high-performance driving.
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