That, or a downstream effect of people applying for jobs for which they do not quite meet the stated qualifications. Putting up "5 years experience" starts being a really good way to get ambitious people who have two or three years of experience, and so employers start using the job description to grab those applicants rather than actually-meeting-qualification.

On second thought, though, it's more likely due to H1B employment requiring an "attempt" to hire a qualified domestic employee. So once an employer has an H1B they want to hire, they have to put out a job description and fail to find an acceptable candidate meeting the listed qualifications.