GOPATH is hated because it's poorly thought-out. It's poorly thought-out because Go is designed by Google, who uses Bazel for dependency management. GOPATH is only there because you can't expect everyone to adopt Bazel in order to adopt Go, so some half-assed solution gets designed to get the language out the door.

In simpler terms, the people who designed the language don't use GOPATH at all. That's why it's terrible.