SE-0361が入ったからです https://github.com/apple/swift-evolution/blob/main/proposals/0361-bound-generic-extensions.md

swift-evolution/0361-bound-generic-extensions.md at main · apple/sw...

This maintains proposals for changes and user-visible enhancements to the Swift Programming Language. - swift-evolution/0361-bound-generic-extensions.md at main · apple/swift-evolution