The answer is simple: They are looking for the perfect candidate. Thing is, the “perfect” candidate does not exist.
Period.
Other reason is HR.
HR is staffed to the gills with bims that never worked a real job, don’t understand job requirements, can’t recognize transferable skills, use software that is spotty (at best) when it comes to pre-screening candidates.
I’ve seen all of this when employed with a major contractor.
-—When I was retiring from the Air Force, I had a 20-something HR bim tell me I had “no major corporate experience” (Really? The USAF at that time had around 600,000 people in it), that while I was a retiring officer I had no leadership experience because I ordered people to do things.
The reason is no one wants to train anymore.
So you want the clone of the guy who just left. Which doesn’t exist.
Government has meddled in personnel decisions to the extent that "hiring wrong" imposes huge penalties on employers. They've become gun-shy. If the government would keep its nose out of things like independent contractor status, straight salary/no benefits compensation, trial-period employment, and flexible part-time/full-time scheduling, America would have millions more people working.
But government does the unions' bidding on these issues, and thus the private hiring process remains highly convoluted and cautious.