As Newman said, the USN carriers only grew because the size of the aircraft aboard them grew. they are still made as small as possible to do the job. Compare them with the RN or USMC carriers, and you'll see the point - those carriers are much smaller, and as a consequence can only carry a small compliment of VSTOL aircraft, which have limited capabilities because of the VSTOL requirements.
Making ships larger than they need to be is folly, not just because of the expense and difficulty in manufacture, and not just because you are reducing the tactical and strategic flexibility of the number oof crew, smaller embarked craft and armaments fitted by not being able to split the unit, but they become impossible to manouever - the linear speeds involved in a rotational movement become enormous, and the ships an crew simply would not cope with it. Look at how the Galactica manouevers on exiting the Ragnar storm to present its armed side to the Basestars; it's just not concievable that a 1-mile ship weighing millions of tons could pitch, yaw or roll that fast without breaking up. Now imagine a much bigger ship - it'd be a sitting duck.