Vladimir said:
As others mentioned, to sound as loud or louder than anything else from the competition. More attention, more popularity, more money. There is absolutely no reason for loudness compression with digital media other than that. Today cars are quieter with better sound insulation than in the 1950s. There is no need for loudness compression for headphones because they also isolate from the environment. Vinyl has lower dynamic range due to physical limitations, not because it's an improvement.
Well, I guess it could be usefull if you were driving a convertable '67 Mustang while listening to AM rock stations playing you singles.
I've been doing some measurements with my calibrated sound meter. My car's a 4 door family saloon.
38 to 43 dbs - my listening room with my laptop on and the music off
51 dbs - in my car with the engine on waiting at traffic lights
65 dbs - 30 mph in my car
70 dbs - 60 mph in my car, increasing to 76 db peaks when hitting a bump / pothole in the road
72 dbs - 70 mph on a flat dry asphalt motorway
76 dbs - 70 mph on a flat dry concrete motorway
75 dbs - 70 mph uphill section of asphalt motorway
I've not measured it yet on an uphill section of concreted motorway into a heavy wind with it raining heavily or falling hail stones at 50 to 70 mph.
78 db peaks - listening to Radio 2 at my normal listening levels whilst doing 70 mph on a flat ashpalt motorway.
The least compressed CD I have is Rickie Lee Jones Flying Cowboys. It has a DR of 17. During the 10th track of this album I measured a minimum of 48 dbs and a maximum of about 80 dbs at my listening position at home with the volume turned up as high as I would ever want with this album. That's a dynamic range of about 32 dbs.
This album has too great a dynamic range for me to listen to it whilst driving along the motorway without me either turning up the volume 20 dbs louder than I'd normally listen at (no way am I going to do that. Far too loud!) or without me losing the quieter bits in background noise, or without some form of compression.