If there's a particular paper you're interested in, you can usually email the lead author(s) and just ask for a copy. I've never heard of someone saying no, esp

If there's a particular paper you're interested in, you can usually email the lead author(s) and just ask for a copy. I've never heard of someone saying no, especially since it's as easy as emailing a PDF. As for the why -- just DuckDuckGo "why is science behind a paywall" and you'll get a million hits, each author giving a slightly tweaked definition of "it's a holdover from the days of publishing in print journals".