Not that I disagree with the thrust of your post, but is the bolded really true? Why would they prefer a NFL scouting job to being the face of the draft for ESPN? I bet they get paid better, and get national fame and attention to boot. They have more job security than any scout in the business. Their real talent is their ability to be convincing talking heads, a skill which doesn't change while scouting departments will have up and down years, The difference between the best and worst draft prognosticators is only on the margins - so it's not obvious to anyone that they're not much better or worse than anyone else out there.
This comes up every year, but it's definitely worth noting. Guys like Kiper and McShay watch a lot of football and know a lot about the players, but ultimately if they were as good at their job as they lead you to believe on air, they'd have a job doing this in the NFL.
If they become scouts, they get judged by their recommendations and their results, like everyone else. Why would they want that? I bet scouts want to be Kiper/McShay, not the other way around.