There's a fairly active Go project on GitHub that's not found on go.dev so there might be others.
smartcontractkit/chainlink has 6 releases this year, 42 contributors, and 9,372 commits.

Just a hunch: could this be related to the project install using git clone instead of go get?
What did you expect to see?
smartcontractkit/chainlink existing on go.dev.
What did you see instead?
smartcontractkit/chainlink is not found in go.dev.