Well, duh! You only consider skills that people have actually used in a job as skills they possess. Thus the only way people can acquire new skills that will

Well, duh! You only consider skills that people have actually used in a job as skills they possess. Thus the only way people can acquire new skills that will be recognized on a resume is if they end up using them in their current job. It should be obvious that pretty soon the experienced people will fail to be able to include some important skill on their resume. Presto, a "shortage" of qualified people. Employers are so obsessed with hiring the best person that they overlook plenty of people who could do the job.