In reply to ojannen :
The pull: They’re coooool.
Okay, really, here’s some history as I recall it. This is off the top of my head, so feel free to correct.
Back in the day–so we’re talking ’60s and ’70s–the SCCA offered Production classes and Sedan classes for production-based cars. Two-seat sports cars landed in Production, and sedans ran in, yep, the Sedan classes. Each category featured a few classes: A Production (big-block Cobras and Corvettes), B Production (small-block V8s, Shelby GT350 since it didn’t have a back seat), C Sedan, D, Sedan, etc. (Sidebar: Showroom Stock appeared in the very early ’70s, but let’s ignore that for now.)
Sticking with the just Sedan classes, A Sedan featured your pony cars: Mustang, Camaro, etc. Basically Trans-Am-type cars.
B Sedan welcomed your Datsun 510s, Alfa GTVs, BMW 2002, etc. More or less your 2.5L T/A cars.
And C and D Sedan featured your really small-bore cars: Minis, some Alfas, various Datsuns, little Fiats, etc.
The SCCA eventually replaced the Sedan category with the GT category and, at that point, allowed people to run tube-frame cars. Part of the reason, as I recall, was easier crash repair plus the ability to update the body (to keep manufacturers happy).
Nissan, for example, would rather see someone run a current Sentra than an old B210. That Sentra might still run an old-school engine, but at least it looked current. At a time, Nissan and a few others were really involved in SCCA Club Racing. This could also allow a driver to (sort of easily) turn a tube-frame Toyota into a tube-frame Mazda–keep the chassis but change the engine and fiberglass bodywork.
So, that’s how we got to a point in time where tube-frame Sentras were a thing.
Hope you enjoyed my TED Talk. :)