Another good find! You're good at thisThis was my first thought. If they’ve been moved around for various reasons over the years, potentially without much care, then that may very well have contributed to their decay.
Also found this discussion about the switch to HD in the later seasons.

Yeah, all HD cameras and monitors by the looks of things. I think previous seasons were 4:3 cropped to 16:9 to produce a faux "widescreen" that was broadcast.
There's a good chance they switched to DV (remember MiniDV camcorders?) - even still, those are magnetic tapes too.