I'll tell you why. Employers want to pay you the minimal amount as possible.. And when you have people with lots of exp, they dont want to pay you any more. So jobs are not getting filled because the employers/recruiters is being cheap. Costs of EVERYTHING else have gone up, but our wages. I.E I'm currently being underpaid for having almost 20 years in IT.
This is only a problem when employers refuse to hire junior developers. If employers were willing to train junior staff members, this problem would vanish overnight.