A few years ago I had a Mac floppy from the 90's I could no longer read but wanted to retrieve a file from. I sent it to a data recovery service that had high expectations of success, but they failed too. It was so disappointing.
When I used floppy disks routinely, their lifespan was a matter of months if they were used regularly. For stuff I was working on daily, I would always save it twice to separate disks. I'd be fortunate to get through a school term without having disk errors, so I learned pretty quickly the value of having multiple copies.
For stuff that was just archives, saved and then rarely accessed, they would survive longer. My guess is just that the read/write heads were fairly abrasive and wore down the magnetic layer of the disks pretty quickly under heavy use.
Your experience is very different from mine. I used floppies with favorite games and such on them for at least 3 years pretty regularly when I was in high school/early uni in the mid 80's. And I can't remember EVER actually having disk errors in school with homework and such on them. Possibly I did, but I'd think losing that critical piece of homework would have stuck with me.