Edit: Just to add.. some entire runs of magazines are being destroyed: nudist magazines from the 50s-80s are almost entirely being burned, because while they are legal, they exist on a borderline that can easily imprison someone. I know of one library that has hoarded 14,000 issues and scanned every one of them but does not allow access since the optics on such magazines is so maligned.
I know I have copies of some niche things that aren't online anywhere as far as I know--and, absent digitization and upload--will presumably fade from existence at some point.
If I had the space I would take every one of them, but I don't right now. Maybe in a few months. I'm going to start trying to raise capital to take them all and scan all the missing ones. Most magazines in existence are now copyright orphans.
The question would be how many of those are magazines which need preserving. You'd be wasting your time scanning old issues of National Geographic, for instance; there are already comprehensive archives of those.
There are a number of magazines I would pay for the archives and they may well exist but I can't access them anywhere.
Think "college-adjacent" run off the mimeograph machine late at night kind of thing. They could have run for 4 years or more, and basically be forgotten.
Now and then you hear of a famous author's work being rediscovered in one, from something they wrote in college for one of those magazines.