Pedals wear. I’ve worn through the pedal body on a couple of pairs, also the sprung part of the mechanism where the cleat locates gradually wears away so that the cleat isn’t held as securely. I used to cannibalise cheaper SPD models to maintain the performance of my more expensive but worn ones. So it may be the pedals as much or more than the cleats.
I don’t think the materials are as good as in the days of yore. I used to have to slacken the tension on spds when new but the last two pairs I bought seemed to have barely enough spring tension in the tightest position. Whether this is deliberate or a decline in accuracy in the pedal or cleat, I don’t know
Back in the day they used to last 5+ years a time.
I had attributed their shorter life span to the advent of markedly more technical riding and body English on my part since 2013, but maybe the materials are different now. Certainly my pedal bodies have also worn quicker from about the same time.