I'd sum up that train of thought like this... A recruiter who comes back to the hiring manager with "this person is a superstar at [competitor] and we can steal

I'd sum up that train of thought like this... A recruiter who comes back to the hiring manager with "this person is a superstar at [competitor] and we can steal them away" is a more persuasive argument, as well as a feather-in-the-cap for the recruiter, as opposed to, "this person is, well, Open To Work at the present time." At the very least, in the first case, you have to move quickly, which is desirable to the recruiter. Or another way: imagine visiting a foreign city and there is an extremely busy restaurant and a mostly empty one. You're likely to go to the busy one first and ask if it's possible to get a table... the hostess says "normally no, but we just had a cancellation and its yours right now." Score! A story you'll tell all your friends. Getting a table at the empty restaurant... ehhh, whatever.