EDIT: Not sure why this is getting downvoted. Look at the ad copy of some of these cars. https://www.ford.com/cars/mustang/ Literally the first line is "Hear the roar of a Mustang..."
Add to that ecological requirements and you have a very tight margin that car manufacturer can tweak in.
Also just because car can sound loud when driven in full throttle, doesn't mean it has to. It is on the driver if he chooses to be a nuisance, not manufacturer(Straight piping an old beater car is dirt cheap, having a hole in exhaust is even 'cheaper' and is much louder than any of the expensive, performance oriented cars in question.
You do need some back-pressure to siphon back, but the amount is very limited, especially when we compare it to the sheer amount of air mass that those cars are moving.
Just so it doesn’t get lost — my point is, sports cars being loud when they’re full throttle is not a problem and never was, realistically you wouldn’t drive them that way outside of a racing track anyway. The fact that people still do it and annoy everyone else is a people problem, not a car problem.