I don't think its really about people keeping their devices long. One of the most appealing aspects of buying a mac is their longevity. I think it's more to do

I don't think its really about people keeping their devices long. One of the most appealing aspects of buying a mac is their longevity. I think it's more to do with newer macs being more iterative and also the Apple Silicon being fully integrated into the whole product stack. The jump from Intel to M1 was huge, but M2 and M3 have been more iterative, at the same time everyone who wants an Apple Silicon Mac probably has one by now, so the iterative upgrades of M2 & M3 aren't really that meaningful.