It's not like UCAVs aren't being developed, though. Piloted aircraft have lower latency and are better for some tasks. If UAVs were ready to replace piloted aircraft in all combat roles, they would have. They have almost completely replaced piloted aircraft in ISR, for example, where they are a great fit (no Gary Powers, no latency issues). The Pentagon doesn't want to lose trained pilots.

Does it justify the expense and the shortcomings though? Horses also have some advantages over tanks, like refueling from the grass on the roadside but they become mostly ceremonial anyway.