It’s all about turbo sizing and the complexity of doing a turbo system on a V8. If you use small turbos, lets say a pair of Garrett GTX2871 with a .48ar turbine housing on moderate boost you may see somewhere like 650-700 hp from a LS1 engine and torque should be around considerably higher and from a much lower RPM(about 1200 rpm). Manufacturers have to look at power to weight ratios of their vehicles as well as fuel consumption.
Is far as supercharging its way simpler than turbocharging to install and tune from a factory prospective. No need to change exhaust manigold and the evhaust system dramatically, which saves money. You also maintain a N/A like power band and engine response.
There is not really sucj a thing as turbo lag either it all depends on how eell the turbo is sized for the application. On a good sized turbo configuration you can produce max boost pressure at lets say 2200-2500rpm which aids torque production. Compared to a supercharged application where your max boost is produced at the maximum engine RPM because the blower has a directly coupled to engine RPM.
There are a fair bit of turbo american car models. But usually on smaller engines.
The reason you see superchargers on things like mustangs and camaros is because they are usually roots style blowers and are simple. On V engines they can usually put them in the valley of the V so they dont take up a ton more space and theres no ducting, intercoolers etc. They also provide instant boost and more predictable/linear power gains across the rpm band.
Because you have large v engines, which automatically make a lot more torque compared to europeans/japan. And because superchargers take away about 40% engine power in order to make more, try taking 40% away from a 1.8L.