IMO, its natural that many players, even the oldies quit the game. Not only BC but other games as well. For example, I used to play GMS but I quit as well after 3 years cause it gets bored playing the same game and same thing over and over. Yes, there might be updates and events going on and players will play back for maybe another 2-3 mths (in my opinion) and quit again.
For BC, it was crowded during the last yr's christmas event and it gets lesser and lesser after few mths. When the 258 map was introduced, many played again (leeching and so forth) for that map. And bcuz of this map was introduced, many has been able to get to 225 in jus few weeks or so, depending how long the grinding goes. AND then quit AGAIN after reaching the max level (w/o member).
For me, even I just joined BC during last yr's July or so, I started to get bored as well now. I might not quit but will not be as active as I used to be.