You’re oversimplifying the alignment angles. Let me try to clarify. Caster in itself does not cause any kind of tire wear. But, in cars that specify a high amount of caster, the camber angle changes drastically as soon as the steering wheel is moved from the neutral position. So much so that a car that has negative camber straight ahead will exhibit wildly positive caster (and very accelerated tire wear) when turning. A typical family sedan may have a caster angle of +3*. I’m talking about cars with +9* or +10*.
This combination of angles results in very snappy and responsive steering, great road feel, and excellent handling during aggressive maneuvers. The price to pay for these things is that the outer edges of your tires may wear to the cords in 20,000 miles. And the wear is most noticeable on cars that are driven primarily in urban settings, such as turning from one street to another and in and out of parking lots all day.
Now none of this affects the typical Subaru, Honda, or Chevy driver. But to the people out there who say there’s a defect in the car because their sport sedan wears out tires quickly, I say the car is operating as designed. And that’s where the discussion started, I believe.