BSD is about being kind to everyone, even unkind people.
GPL is about being kind to everyone, as long as they are as kind as you. When sharing something valuable under a GPL license, you’re incentivizing others to be kind like you.
Obviously, if you’re a millionaire like Carmack, you don’t need others’ kindness to get by, so from his point of view a BSD license is better, as his goal is simply to disseminate his code as widely as possible.