I'm more interested in why people are interested in the Pennsylvania, after it hasn't existed since 1968?
Mark:
Possibly because the PRR served the most populous and industrialized part of the country. More people were affected by the PRR than any other railroad. And it was at one time the largest and richest railroad in the world. That resulted in the PRR developing a large following.
I model the PRR because I grew up living between the Philadelphia - Washington Main Line, and the Chester & Philadelphia Branch so I was immersed in things Pennsy. I also worked for the Pennsy, from January 31, 1967, through January 31, 1968. That's why I personally model the PRR.
The PRR is many things to many modelers and fans, Steam, Electric, Transition, and post 1966 (which I model). Mainline Passenger, and Freight, Commuter and Branchline, Yards and Terminals etc., all of which were well documented, photographed and easy to replicate.
The fanbase, is sometimes rabid, but also diverse, and obviously affluent, which is why so many PRR toys are manufactured and imported.
Boris