#1 they dont. Its mostly the roll they want to get rid of. But they still want movement so the wheels are in constant contact (grip) with the road. Ridged bars dont do that. Drifters however may as well go the bars.
#2 expence, size, weight, engineering complexity, rev happy no torque, and they have the tech these days to not need to. Look 1.6L engines are making more power than V8s were 30 years ago (obviously stock for stock)
#3 If you went to a concert and the band was standing up the front, but the sound was coming from behind you... The idea of the stereo is to attempt to recreat real life, ie sound from infront of you, such as it would be live and unpluged. As in singers voice up front in the middle, drums up back and spread out a bit, etc etc. If its in the back you just wont get that.
#4 WRC cars still need to be road registered. And in some cases the police have stepped in if they are speeding between competive stages, if the car is just that smashed up etc. Also, can you imagion anti-lag in an engine bay full of wires and hoses?