Why are hub carriers toed in different angles for rear wheels?This seems like it would just wear down tires faster rather than have any handling benefit.Plus it looks funny

rear toe-in improves straight line stability. If you had zero degrees of rear toe-in, you will have a hard time to accelerate in a straight line.

even with AWD?

Yes. Without rear toe-in, the rear end will drift. With zero degrees of rear toe-in, the car will shimmy and even fish tail when accelerating hard in less than ideal traction conditions. I run 3 degrees of rear toe on my 1/8 scale buggies and 2 degrees for my nitro and electric sedans.