But signing is largely a moot point as people will follow the instructions on the website where a clever attacker would simply create their own cryptographic keys sign it and provide instructions for adding it to your keychain to the compromised website. Public key crypto does not solve establishing trust for an actor. It can only do so through delegation which as we have seen with the deprecation of EV certificates (CAs no longer being trusted to establish the identity of legal persons) is not something that is easy to get right.
Certainly it is better to trust the maintainers of your operating system/package manager than a random website. However they only sign things where they have done due-diligence on the project, which is a slow process, too slow for projects with faster release cycle such as Docker or Rust.