There were a reason in history.
The first practical transistors were mostly PNP, especially in the early 1950s.
Quick why-this-happened version:
Early semiconductor tech worked better with germanium
PNP transistors were easier to manufacture with the purity and fabrication methods available at the time
They had better performance and yield than early NPNs

boss did it like they did so that the ubiquitous switching dc jack could be used to disconnect the positive lead of a battery when on an adaptor, while also disconnecting the negative lead of the battery with the 1/4″ TRS input jack. mostly cause it was the cheapest way to achieve both for mass production.

IIRC it’s Boss’s fault for trying to be different but then everyone adapted to it.