Because iOS 14.5 -if I remember correctly- had bluetooth issues. So I waited for the next one. And I don’t remember what issues had 14.6, I guess it was battery life? The famous battery draining problem. So I waited to the next one. Then, iOS 14.7 seemed better than any other, but many people were reporting WiFi, data and cell signal issues, dropping calls and having to enter airplane mode to switch from WiFi to 4G. So I waited for the next one... Then iOS 14.8 showed an even higher battery drain, so I... (you know the rest)
Honestly, my expectations with iOS are that every major release will be better, faster and more stable. However, with iOS 14, it seemed like every time they fixed one thing, they broke another one. So I’ve been always waiting, on the verge of the update.
At this point, and if iOS 15.2 isn’t a catastrophically bad release, I will update all my devices to it. Christmas releases tend to be pretty polished because people buy a lot of devices during this time of the year, and Apple knows that.