If you were casting actors for a play, would you rather hit each candidate with a surprise audition five minutes after they got out of bed, or give them time to review the lines and stretch their vocal cords?
That's not a fair comparison at all. Interviewees know well in advance of when the interview will happen. A more apt comparison would be telling an actor what script to use for the audition vs giving them a script they've never seen before at the time of auditioning. This still isn't a fair comparison though because they're testing acting talent, not the specific script. A good actor can learn the script.