CoD players left because RO2 is: ugly, buggy, slow paced, boring, has small community/playerbase, "german AK" isn't that fun like CoD's AK, too difficult, maps are way too big, game doesn't have enough unlocks and again game looks like CoD 2.
BF players left because RO2 isn't even half as good as Battlefield 3 (why the hell BF players would pick RO2 over BF3 ?!).
New customers* were looking for original, WWII tactical combat experience in RO 2, something new and different than "modern warfare" games, but they got cheap and lame CoD clone.
RO players* were looking for improved, better looking RO:O/DH with new features like mantling, bullet penetration, etc real and better successor of award winning Red Orchestra series, but they got cheap and lame CoD clone.
I posted it before but take a note how HoS is similar regarding gameplay to CoD WaW
Call of Duty - World at War ( PC Multiplayer ) - YouTube
*) TWI should create a game for these guys, because they never make a game better than CoD or BF to please other guys.