I don't think you have been looking at freight car trucks closely enough. Perhaps the variations are sometimes a litle more subtle, but they definitely exist.
John
There are articles in old MR issues.
Here's the google search results for freight trucks:
https://www.google.com/search?espv=2&q=freight+car+trucks&oq=freight+car+trucks&gs_l=serp.3..0l2j0i22i30l8.12139.20464.0.21301.57.32.0.2.2.0.163.3540.8j23.31.0....0...1c.1.64.serp..33.23.2459.0.b5sJN-xLMAs
Here's the google results for passenger;
https://www.google.com/search?espv=2&q=passenger+car+trucks&oq=passenger+car+trucks&gs_l=serp.3..0j0i7i30j0i30j0i5i30l7.148841.153436.0.156558.16.16.0.0.0.0.251.2132.4j10j2.16.0....0...1c.1.64.serp..0.16.2123.XDA6aFtVV5M
If you're an optimist, you can search with Windows 10 "Edge" (good luck).
Paul
Modeling HO with a transition era UP bent