Mine generally last a two years or so, before they are scratched and fogged to the point that my vision is affected. The big culprit is dust - often metal dust, but also hardwood dust - in the shop. Even if you religiously use a non-scratching, micro-fiber wipe (which is hard), just dragging the stuff across the lenses damages them. Another culprit is glue, particularly CA (super) glue but also other types. You may not think it would end up on your glasses, but if you're using much of it, eventually microdroplets end up on your lenses. This does immediate, permanent damage to polycarbonate lenses.
My desk glasses, optimized for computer screen distance and never actually leaving my office, on the other hand - easily last a decade with no discernable damage. Because - no significant dust, no organic vapors, no glue, and always wiped with a clean micro-fiber wipe.
For me it’s always been chlorine and other cleaning products. Salt water and sweat doesn’t help either.
Forget to take the glasses off before you jump into the pool or readjust your glasses while cleaning the house and before you know it the coating starts to dissolve. Even if you’re religiously rinsing them, the accumulated damage to the coatings fogs up the lenses and weakens the surface against scratches.
That removes way less than all of the abrasive dust, and to some extent just turns what remains in to an abrasive slurry. You still get abrasion of the coating over time. And water doesn't help at all with damage due to solvents, glue, and the like.
My desk glasses, optimized for computer screen distance and never actually leaving my office, on the other hand - easily last a decade with no discernable damage. Because - no significant dust, no organic vapors, no glue, and always wiped with a clean micro-fiber wipe.