I've been a photographer since I was a little boy. I remember shooting on old 110 film cartridges when I was maybe eight or nine. I got my first real camera when I was 11: a Minolta X-700. I shot with that for many many years and I still have basically all of the pictures I've taken.
I also have most of the negatives.
At heart I'm an archivist. It's really kind of weird, honestly. It's something that I've always really had in my soul for some reason. I still have nearly every email that I have ever recieved in my life (spam and ads excluded obviously).
The funny thing about this is that most people seem to have gotten rid of the negatives and just kept around the prints they got back from the developer.
Slides, on the other hand, are the thing that's important, so people instinctively seemed to have kept those around. I'm guessing they were stored in the closet of a spare bedroom or maybe in the basement or attic of their house. They kept them until they died, probably having not looked at them for years or even decades. My theory is their kids were selling things off.
The thing that's so compelling for me about slides is that they are the original piece of film that was loaded in the camera and it was right there when the photo was taken. The light that was bouncing off the subject, through the lens, and hit the film was captured by the emulsion of the slide and is directly involved with making the images that they contain and you can see on this site.
Since they are the orginal they have the highest fidelity of possible. Unlike prints which fundamentally are copies of the original negative (or slide I suppose), the slides I have are the original.
Incidentally, since I'm in possesion of the original I now control making copies of the original which is why I'm allowed to present these to the public.