Usually because of dust and years of filth from your hands. You have to clean your mouse and wash your hands after visiting the shitter. A more common problem is driver related issues, unplug and plug it in again or reinstall the broken driver. Also don't use wireless, their battery will only last for ~5-10 years on average.
I have a box of trackball mice, none of them are broken, they're just not as accurate as laser mouse. Mousemats are still a good thing to have for better accuracy, keep that one clean as well.
Yep, I have one of those too, still works surprisingly. They don't make them like they used to. But on the other hand, it's very hard to add (((planned obsolesce))) to a mouse or a mousemat.
But thanks for the advice
https://eintr.net/systems/sun/kbd-type5c-mouse-type5/pi/5.jpg