Simple: server space and loading time. Any additions that slow the game down are to be avoided.
If you want a "soundtrack," might I suggest you go to Youtube and create your own playlist of WW2-era songs?
Here's a few suggested songs to include:
1. Panzerlied -- Germany
2. White Cliffs of Dover -- Britain
3. White Christmas -- United States
4. Lili Marlene -- Germany, Britain
5. Colonel Bogey March -- Britain
6. Hitler Has Only One Got Ball -- Britain
7. Boogie Woogie Bugle Boy -- United States
8. Scotland the Brave -- Britain
9. Der Fuehrer's Face -- United States
10. Erika -- Germany
11. The Navy Hymn -- Britain, United States
12. Der Koeniggraetzer Marsch
