This is after 3 seasons which include riding rollers and Wahoo during winter.

I may have figured out what is going on here. When I walk with the above shoes on, I walk flat footed. I do not walk as if I am in standard shoes. The cleats only make flat contact with the ground. This may help explain how I can get such long life from a set of cleats. When I rode Look pedals I got 6-7 years out of a set of cleats. Since the Shimano pedals are relatively new to me and I am going into season 4 with them it is likely I will see the same service life from the Shimano cleats as I did with the Look cleats.