Here's a reason nobody has covered yet: Government department wants to hire a specific person for an open position. Due to public service hiring rules, they can't do that. They need to have a competition and look at all applicable candidates. But they already have who they want on contract, and getting the person into that position is the desired outcome. (Also, NOT getting that person results in several years of experience waking out the door when the contract ends.)
Solution? Figure out every single thing that person knows, and make the requirements match that list as much as possible. That results in requirements that seem silly and in some cases don't actually even line up well with what the job requirements are, but they also ensure that the person they want is almost definitely the one who meets them.