Because when you join european and American servers you cause misery for everyone else on the server.
As an American myself who has played in NA and outside this just isn't true, a higher ping affects us more than it affects you. Your latency is effected by YOUR proximity to the server, not mine, that's how the netcode and interpolation works.
It's also very selfish to argue the rest of the planet shouldn't enjoy the game because of some made-up concern you've literally never experienced with BF. We've been doing it in every single BF prior to 2042 without causing you "misery." Hell even in 2042 if you count Portal lobbies.
Not to mention every major online multiplayer game allows for some flexibility in region if not outright selection options in the settings. This is to account for their players in low population regions.
