Once the M5 went AWD BMW was saying that the RWD package was now obsolete due to engine power. I am sure with the M4 they did not want to see this but were slow on getting the AWD package together.
https://youtu.be/4CB_cKA9kxE
M4 - RS5 - AMG C63S EURO Spec
https://youtu.be/t1JNuMgKaSA
M4 - RS5 - AMG C63S USA/CA Spec
Skip ahead the yacking to the first the standing start then the roll. The M4 is obviously the choice for power but getting in to the ground is difficult.
Bet 95%+ of the M4's will never turn a wheel on a track but will have some traffic light Grand Prix. Hate to see the M4 dumped by a car with less power but more traction simple because its RWD.