To the question of how many modelers chose to model eastern vs western roads, I don’t think we have any way to know.
But the manufactruring bias is clearly in favor of western roads with only one exception - the Pennsylvania.
It is easy for a manufacturer making an F7 or a USRA steamer to include all the road names that are approperate to that prototype.
But look at the specialized, prototype specific models:
Con Cor did the Burlington Zypher but not the Flying Yankee
We have our chioce of GS4’s and Daylight cars but not one mass produced acurate B&O name train and its matching locos.
We have our chioce of UP Big Boys and Challengers but no B&O EM1 or EL locos? Only one mass produced C&O H8 - now out of production?
And the south east roads are really shuned - only in the pre Walthers years of Proto2000 was there any attempt to offer some south east roads on diesel locos.
Sure, we have N&W “J”'s, the Y6b and the Class A, while long lists of other notable east coast steam has never been produced or only offered a few times in brass over a 40-50 year span of time.
But from where I sit there is plenty of UP, ATSF, Milwaulkee, SP, CB&Q - and lots of it is very road specific.
2-10-4’s and 2-12-4’s but no B&O 2-10-2 S1a?
Only a few “famous” steam locos from the NYC, but what about the Southern, RF&P, ACL, Seaboard, Wabash, and others.
Right now, or even in the last 10 years, the only B&O steam other than brass has been “also ran by other roads” stuff like USRA Mikes. Yet they where the nations first railroad - and a very big one at one point - Baltimore to Cincinnati to Chicago to New York is no small area. And the B&O had a large and interesting fleet of of steam - like their home built 4-8-2’s that performed so well they never even thought about a 4-8-4 or 2-8-4.
I can buy Milwaukee proto specific box cars and cabooses mass produced by the sub class, but only one mas