Why does not Google count open redirects as a security vulnerability?

I was surprised to learn that Google does not count open redirects as a vulnerability and is not valid for your error rewards program. Open redirects exploit the trust between a company (Google in this case) and its users, this definitely seems to me a valid vulnerability. I was even more surprised when I found this.

Why does not Google, one of the most secure companies, count open redirects as a security vulnerability?