Because I have expertise that the last few PMs didn't.
First batch were non-technical, which can be crippling with highly technical projects.
Second batch were *too* technical, which meant they didn't know how to be diplomatic with the client and got upset too easily.
I've got the technical background to understand the intricacies of the project, a thick skin from years of being yelled at by people with guns and power, and the ability to be diplomatic from years of working with Federal bureaucracy. Once you've been verbally reamed by somebody who's only three steps below the President on an org chart....everything else is low-pressure.
Also, the projects failed before (at least the second time) because the client balked at the price tag and decided to postpone. Now, the support envelope is running out so they don't really have a choice. This *has* to get done, and so even if they grumble about the cost, they can't kill it because of budget unless it gets ridiculous. They could have gotten it done considerably cheaper if they had started a couple of years ago, but hey -- them's the breaks.
Admittedly, you could be right and I might be out of work again in six months. If so, then *shrug* I was going to be laid off anyways. This just netted me six more months of paycheck and a bit more severance if/when that happens. Because of that, I don't really have any fear (which is, IMHO, another reason I got it -- all the established PMs didn't want to touch it with a ten-foot-pole). And they all have other projects they're already working on. They wanted somebody that could be 100% allocated to this project.