I don't think it's that surprising that such items are being discarded today.
They might have had value at some point in the past, but they probably haven't retained that value well at all.
For example, enough of the information in those encyclopedia sets, non-fiction books, and magazines is probably now out-of-date, invalid, wrong, or incomplete.
Most of the paperback books and magazines I've seen discarded in boxes along sidewalks are merely previous generations' equivalents of "cheap short term attention catching hooks" from when such things inherently required more physical overhead.
A good chunk of those items probably weren't particularly wanted to begin with, or are infeasible to keep now. No replacements are needed or wanted.
Some of the books, tapes, devices, and other items were probably given as birthday, Christmas, graduation, etc., gifts. They might not have even been that useful to the recipients to begin with. Physical gift-giving like that is less-common these days in my experience, with gift cards and even cash replacing physical items. A lot of items given as gifts in the past are simply no longer offered for sale today, or are so cheap that giving them can even be seen as insulting by some people.
Much of the new housing stock in places like Canada, Europe, and even the US to a lesser extent are small apartments. A lot of people just don't have space for items in general, especially when downsizing or moving into a retirement or care facility.
Enough of the items I see discarded are also damaged, broken, or otherwise unusable, too.