Sound Wave assets seem to have the RF_Standalone flag upon import? Is there a reason for that?

I’ve been trying to load/unload sound wave assets at runtime to keep memory usage low (via FStreamableManager), and realized that they never get garbage collected, even though there are no more references to them.
After having a look with the debugger I realized that the sound wave assets all seem to have the RF_Standalone UObject flag, which excludes them from garbage collection. Is there a technical reason for having that flag set for sound waves?

If yes, how can one cope with a list containing dozens of high quality sound assets, regarding memory usage?

RF_Standalone only excludes things from GC in the editor, and it is applied to all assets, not just sounds.

It doesn’t affect the game.