I can think of two main causes for this: slow response times from recruiters/hiring managers and less than competitive offers. Advertising a job opening is no different than selling any product. If you can't attract customers, make a better product.

We've been hiring for maintenance techs for two months.   Since we're government subsidized, we can't compete with communities who pay $27 an hour and offer an apartment.  Nevertheless, its just plain rude to agree to an interview and never show up.  Or accept a job, go to the clinic for a physical and drug test and never show up for the first day of work.   It's pretty hard to provide good service to low income seniors when we don't have any maintenance staff.  Even to contract out for services is a non-starter.  It takes a plumber a week to arrive for a leaking pipe.

been this way for as long as i can remember. its not just covid related

So crazy. You do a phone interview set up the appointment they confirm and then don’t show! I had one not even show for his first day of work!!!!

It's so annoying. I schedule all my interviews in one or two days if possible and only 50% have been showing up.

We scheduled an interview for a maintenance man and he never showed up… Called the next day and explained what happened so we gave him another chance. Didn’t show up AGAIN