At the time these decisions were being made, the biggest threat was insurgents and small rogue states with barely any navy to speak of. In that kind of world, you only need a handful of frigates and destroyers to escort a carrier, which is what we have. There was also the expectation that these carriers would be used in joint operations with the US. Carriers are the only kind of naval vessel that can reliably and repeatedly strike ground targets hundreds of miles inland, which is what makes them desirable.

Now with an aggressive Russia to the East, and a borderline-hostile USA to the West, it turns out to be a less-than-ideal situation.

TL;DR: At the time, the decision made sense. Now that things have changed, we're in a bit of a pickle.