All of a/c design is a compromise, buffetted by conflicting demands eg efficiency, strength, simplicity, robustness, maintainability & cost. Even marketing & the lawyers gets a look in.
The final design choices are usually after an iterative process that merges on an acceptable compromise that can do the job adequately.
There are advantages and disadvantages to Piper's tailplane solution, just like there are for Cessna's chosen method. Whatever swayed Piper to choose an all-flying tailplane, they obviously thought it had benefits for Piper. Cessna felt otherwise. For Piper the deciding factor could have been something mundane such as perceived marketing ploy or something more technical.