I think it's because in BF there's artillery, tanks, support vehicles etc that lead to more teamwork etc.

On the old BF game I played on PC, you could actually hop in a bomber plane and tear shit up.

The BF framerate is 30 fps, which leads to "bigger picture" stuff ie blowing up buildings, rocket launchers, air strikes etc.

COD framerate is 60 fps which is more designed for close quarters, speedy combat.

I'm siding with BF for now.