One’s for driving the ship, and one’s for handling all the aircraft, so neither team steps on the others’ toes (which is apparently a problem on single-tower ships).
American Carriers have a Bridge for air ops, a Navigation Bridge, and IIRC a Flag Bridge since an Admiral is onboard, all on the same island but stacked. I’m just guessing but I’d bet there is a land transportation bridge or bridges clearence issue going into and out of port and that’s their workaround for it perhaps.