As part of the discussion here: #8820 (comment).

We want to recommend clients use the readonly flag as an indicator if they can send a command to a replica. Since this command was intended to fill that purpose, it should also get the readonly flag. The script was not marked as RO since it behaved weirdly with scripting, which currently relies on the underlying script calls to do the tracking, and double counting the keys will at the very least result in a crash.

We also don't want EVAL_RO to be included inside of the READONLY category, since it is notorious for causing security issues.