To use a metaphor, all the single door planes are death traps. If you have an obese person in the front RHS, nobody is getting out in a hurry.
I have often wondered about this. I can understand structural reasons for only having one door, although I am sure they can be overcome even by Piper (look at the rear doors in a Saratoga !).
If you decide only to have one door however, why not have it in the pilot side? It is not only Piper, also Mooney, Beech and others, so surely there is a good reason!
The only reason I can see is the "gentleman argument" of the pilot not leaving the airplane in a crash before all passengers are out, but as Peter points out, I can also imagine situations where it would be good to have the pilot out first to be able to pull/ break glass from the outside, etc.
In daily use (i.e. when we are not in a crash, which after all is most days), it is a real pain. My wife hates having to stand freezing on the appron while I do the walk around, etc.....and the time I wanted to double check if the luggage hatch was properly closed, she was thorougly unimpressed.
why, oh why?