I mean this is exactly it, right? If instead of posting a new job, you canvass the people who applied months ago, then anyone who says yes has been out of work for months and will probably accept whatever shitty wages and conditions you offer. You are guaranteed a strong bargaining position.
This a actually worked out for a co-worker. He interviewed for a position and the interview went of like 6 hours. He waited 6 months and never heard anything. He applied for another position at my company. Different team, lower pay and not in his specialized field. He got that job. Another 3 months and the boss for the first job called him and said their initial hire didn't work out and asked if he was still interested.
He laughed and said he was already working but would be interested. The boss asked where he was working. He replied "I'm actually down stairs".
He got the job, more money then the initial offer and he was happy in the new position. Probably an unlikely event and I wouldn't recommend trying to duplicate it.
The odds of somebody who was interested 6 months ago to be interested today are much larger than the ones of any random person. And you already have their contact, and already made some kind of screening.
The amount of malice people go out of their way to put on other people's acts is incredible. Nobody cares about you enough to be out to get you. If you don't want the job, just say it.
Companies absolutely care about their bottom line. I never said this was a personal attack - in fact it's deeply impersonal. And of course they're more likely to be interested if they haven't found work yet, that's exactly my point.