A lot of applicants apply for any job that has their basic skill set mentioned, without understanding how requirements are derived for a job description. Believe it or not, many companies legally *cannot* consider you for a job that you are not qualified for. There are two governing bodies that contribute to this: the EEOC and US Immigration. In the case of the EEOC, Affirmative Action and federal contractors (and that is defined as having *any sort of contract*) have very strict guidelines they need to meet in order to prove that they are considering *all qualified applicants.* Those qualifications must be in writing and companies have to prove a repeatable, auditable process to the federal government that they are doing so. The caveat to that is that they are *only able to consider qualified applicants*.
In the case of Immigration, any company that sponsors visas (*generally* H1-B, E3 or NAFTA TN categories) has to prove to the US Immigration that those employees that they *are* sponsoring are meeting the company and industry standard job titles and job descriptions, and that no US citizens or permanent residents (Green Card holders) are available to fill those roles. Job descriptions must include educational requirements as well as the number of years of experience in the job category. Companies need to be consistent across the board when considering candidates for these positions or they can potentially lose their ability to sponsor those employees. Another fact about these requirements is that open jobs must legally be advertised if a company is considering external applicants.
I have not worked in *any* company in the last six years that does not have all their open positions (meaning positions for which they are actively recruiting external candidates) on their corporate website. So the "hidden job market" is a myth.
It’s absolutely vital to understand that the way recruiters identify candidates is through keyword searching on resumes, which is why it is so *vitally important* to use them effectively and to use a reverse chronological resume so that recruiters and hiring managers can match your skill set to your job history. It’s also the reason why outdated skills are going to be of little value to you in your job hunt. If you are looking to transition back into a career track or industry, try doing volunteer work to help you renew those skills and to give your resume a boost in that direction. Make sure when you are updating your resume that you put volunteer information prominently in your career section. To do this, instead of using "Employment", use "Professional" or "Relevant" Experience as your header. Write it exactly as you would a job entry, and be sure to update your summary/executive summary appropriately. Volunteering is becoming a more vital way of getting experience every day.