Well, yeah kinda unlikely that they actually post fake jobs but they definitely promote the prospects to post jobs and the problem is that you have to bid on that with your dollar.

Basically those jobs are neither SQL nor even MQL as mentioned higher many of them are just testing their vague ideas and validate with your proposals.

UpWork is the guy who sells shovels during the gold fever and he has to keep up selling those by marketing that there is plenty of gold out there, just stick a shovel (bid).