I was wondering this myself 30 seconds ago while reading your post describing the history. The possibilities I came up with were lower speed limit on the nosewheel, or structural weakness wrt. bouncing, etc. And soft fields.
All those factors aside, my ideal conception of a tricycle takeoff is to rotate so as to reach the liftoff attitude at the same time as you reach the liftoff speed. Any sooner, and it's unnecessary induced drag. Any later, and you're using more runway than you need to.