When you are comparing online job boards to employment centres and classifieds, they are more accessible and available. Employment centres always involved making a dedicated trip. Newspapers cost money and may involve a dedicated trip to fetch one. Not to mention that plenty of businesses simply didn't advertise jobs in print, particularly entry level jobs. Part of that may have been expectations: people would actually walk into businesses to drop off applications or see if openings are available. Again, it took a lot more effort to find those jobs.

Fun tidbit, I remember visiting Edmonton (Alberta, Canada) in the early 2010's. Boom times for them. It was a bit like walking into a different era with respect to job seeking since many business (again, entry level jobs) were advertising with help wanted signs in their windows.