It's probably because they technically have to make that job posting and let it sit before handing it off to a contract firm for $300k.

I think so too.

What is stopping somebody who'd be inclined to take a COBOL job from just starting a contract firm and taking the $300k from the government? Does the government check if they actually have employees who have 30 years of COBOL experience before handing out those contracts?

There’s a lot of compliance work involved in getting government contracts.

Also, there’s usually 2-3 layers of pimps (prime and subcontractors) who take a vig at each layer. Total comp for the contractor is usually rate divided by 3 or 4.

Nothing is stopping them; this is exactly what people do.

It's been years since I looked, but mainframe jobs at the big banks in Charlotte were a little less than that.

Whenever I hear about a skills shortage (in any field), I automatically append the phrase "at the salary we want to pay" and that completes the equation.