Mono music files - why?

[madkeim]

I opened the file in audcity and it does appear to be a stereo track.

Technically it is a stereo track (I just checked in my DAW), but the stereo spectrum is so narrow that it feels mono.
I could hear a very slight tiny difference when I switched it in mono, it's almost unnoticeable.
It's pretty much the same for "music_transition_11engine_12streets".
And I agree, mono tracks are wrong most of the time, especially ambient tracks.
It is a mistake in my opinion.
I am not sure I noticed it in game though