Yes, I totally agree. I think there are a constellation of factors that influence the upgrade decisions of users, but I have found it surprising how much the software has been under-discussed following Apple's miss.

If someone was happy enough with their iPhone 5s, 6, or 6s running iOS 11 when the X was released (Fall 2017) then I suspect they didn't feel much more pressure to upgrade when they were running iOS 12 and the Xs was released (Fall 2018).