Is it intended that the configuration of archived LS still keep in nvim-lspconfig?

SSIA.
e.g. sqls (server configurations)

Why not open an issue or PR at nvim-lspconfig about that?

I wasn’t sure if I should make this an issue since it is neither a bug report nor a feature request.

I would like to know if it is intentionally left as a policy or if they are simply unaware of it.

Only way to know is to report it at the repo. (And whether it’s a feature or a bug fix is not really important.)