Why are all low profile tires of high performance design?

I don't understand why all 50 series or lower profile tires have to be H, V, W, or Z speed rated. Why can't they make any of these tires in an S or T speed rating so a person could get 70K-80K miles tread life? Not everyone who buys these tires wants race car tires. Some of us would like to be able to get them in a touring tire.

Probably because most cars that use that profile are sports cars. Its rare to find a sports car with less than a 17" wheel stock.

Actually your question was about the speed rating affecting tire life. Tire life is determined by the compound. A harder compound will last longer. Just because a tire has a high speed rating doesnt mean it wont last. For example my Kumho Ecsta ASX tires are ZR speed rated but are 205/50/15 which isnt that low of a profile. They have a treadwear of 420 which is quite high, and still have decent grip.

Actually your question was about the speed rating affecting tire life. Tire life is determined by the compound. A harder compound will last longer. Just because a tire has a high speed rating doesnt mean it wont last. For example my Kumho Ecsta ASX tires are ZR speed rated but are 205/50/15 which isnt that low of a profile. They have a treadwear of 420 which is quite high, and still have decent grip.

You're right, I did make some mis-statements in my original post. However, it does seem the vast majority of low profile tires are H, V, or Z rated, and most of these tires have a low (200-300 range) treadwear ratings. There are a few with higher (400-ish) ratings, but there seems to be very few of them.