A lifetime appointment does not mean they are not accountable. The federal government was designed with so-called "checks and balances", and impeaching a federal judge is one of those checks and balances. Congress can impeach and remove any federal judge.
> A lifetime appointment does not mean they are not accountable.
Likewise, people getting hired to agency positions doesn’t mean they are not accountable, plus they usually come with domain-specific expertise, and it doesn’t take a literal act of congress to change them.