Your premise and your logic are both flawed.
Premise fail: https://www.apple.com/support/keyboard-service-program-for-mac-notebooks/
Logic fail: Just because Apple introduces new iPhones every year you cannot conclude that anything is wrong with the earlier designs.
Your logic is flawed also.
Usually when Apple addresses a "small percentage" of devices, they don't undergo multiple tweaks and changes which they do not announce beyond talking about sound dampening. Where were the incremental fixes and redesigns for other notorious MacBook flaws (peeling antireflective layer on retina pros for example). The fact that they keep changing the keyboard without really highlighting this is unprecedented for Apple (in terms of their keyboard design history).