That is because most people see the Badge
And believe that it represents the make of car when in actual fact there is very little of that brand involved.
Here the Bathurst 1000 for local Tin Tops Holden GM and Ford use a basic shape of the car for each brand and the engine but everything else is Special some being for safety like Fuel Cells which do not leak in a crash and others like Gearboxes which are Race Specials and where never fitted to any Road Car they where built for racing and the ability to easily change gear ratios quickly for different tracks or car setups.
The Old Ford Diff is still popular or at least was the last time I looked but that was a while ago now as I don't really follow that type of racing other than occasionally looking at some sort of failure and writing a report to prevent that happening again. Things like Fuel Rails for Injector Systems which leak come to mind but there is very little else that even comes close to what is supplied as Production Vehicles. Most do not even start with anything but a Body Shell and build their race cars from that after reworking the basic shell to suit their needs. Things like welding every metal joint get done which simply isn't in any Production Vehicle and all Engine, Transmission and Suspension Mount Points are changed to suit what is being used by that team.
However what really put me off Oval Racing was the crowds who attend as they seem to me to be more interested in the crashes than Motor Racing as to them there is no Motor Racing without big nasty looking crashes. Hence they want to see all of the track so that they miss none of the crashes and make sure that they get a better view of them when they occur.
Of course like the recent one where so many cars came together and mounted the walls a lot will complain that they got injured by bits of car entering the spectator areas. Ideally this should not happen but honestly it's what the majority of spectators want to see.
Col