It was due to the careful and deliberate nature of the Go team, and the backward compatibility guarantee. It took years for the group to put together a proposal

It was due to the careful and deliberate nature of the Go team, and the backward compatibility guarantee. It took years for the group to put together a proposal with minimal changes to the runtime and core libraries, and this implementation in 1.18 will be limited in scope to only add the feature, waiting for future versions to update other core libraries to adapt generics in a backward-compatible way.