I just enjoy new tech and trying new things in that arena. So new phones before I technically need to is one of the things I spend disposable income on when something in that arena catches my interest.
Does have a nice side effect of constantly reenforcing the use of platform agnostic services and retaining ultimate control of my data if it is something I care about, since it really allows me to just move the sim to a new phone and be up and running in a hour or less with more or less any Apple or Android phone.