Can’t say I’ve ever got something directly from a wanted ad, granted wanted ads tend to be for very specific/rare items so tend to be a stab in the dark anyway. I did get a few messages from folks when I had a wanted listing for an MWS but decided not to go for any of them in the end.
I’ve definitely seen others post wanted ads, and then the exact item/RIF they’re after gets listed shortly after... so perhaps they can function as a final nudge of ‘I don’t use this so I’ll list it because it’s worth something’ to would be sellers.
The main ‘risk’ with wanted ads is to be wary of potential scammers. By openly saying what you want you’re putting all your cards on the table for someone who could try and pull a fast one... so that’s another reason that folks may opt for creating a listing rather than directly messaging the person asking.
The wanted ads most commonly marked as complete tend to be for parts, and imagine that’s where they’re most effective. Most folks have bits boxes full of shite that is precisely what someone else is looking for.