The RN didn't require Carriers for the defence of its empire. The only time you need carriers is when you haven't got airfields capable of hitting the area. If you're defending land that has airfields, like Australia. You don't need carriers to defend it.
If the RN was taking the fight across the small islands, then carriers would have been needed but America was doing that part. In the Atlantic we had the carriers needed, we weren't going up against other big carrier Navies, so why build masses of them of our own?
If the RN was taking the fight across the small islands, then carriers would have been needed but America was doing that part. In the Atlantic we had the carriers needed, we weren't going up against other big carrier Navies, so why build masses of them of our own?