Why Combat Training Has Changed So Much

@ GPS guided bombs. These made supplying firepower for ground troops safer, easier and much more effective. When possible, the air force likes to send in a heavy bomber (B-52, B-1, B-2), which carries enough bombs, and can stay in the air long enough, to support many troops down below. But often it's a fighter (F-15, F-16, F-18) pilot who gets called in. These smart bombs have taken all the excitement out of close air support, although improved cannon fire control systems  makes it practical for fighters to come down low and shoot stuff. But commanders don't much care for that, as it exposes the expensive aircraft to unnecessary risk. Most smart bombs are dropped from 3,000-6,000 meters up. That's safe from ground fire. Training for this sort of thing can be just as easily done on the ground. 

@ High Resolution targeting pods. These pods, which contain day and night vision, with magnification, for pilots to spot targets, and a laser designator to allow for the use of smart bombs, have been around for two decades. The current generation of pods allows pilots 6,000 meters up, to make out individuals on the ground, and whether they are armed. This has made fighter pilots, and their pods, very popular with the troops below. The pilots like this because it gives them something to do, and often finds them a target they can pop with a smart bomb, or maybe even (rarely) a strafing run. But, alas, this is also something that can be trained for on the ground, in a simulator. 

@ Programmable Electronics- This had made electronic warfare more important, because there are more electronic warfare pods available, and the newer pods can be reprogrammed to deal with new threats. Enemy air defenses can possess a wide array of missiles and radar controlled guns, which can only be taken out with the help of these pods, and special missiles (like HARM). More pilots, not just electronic warfare specialists, are now expected to go in and deal with thick enemy defenses. Alas, it's another geek fest when it comes to training, and can be done well on the ground.

@ UAVs- There are a lot more of these now. Often there many more UAVs in the air, than manned aircraft. This relieves pilots of some of the more dangerous, or boring, missions. But pilots have to learn how to coexist up there with UAVs, and work with them. 

All these changes have required fighter pilots to spend a lot of their time training and adapting to these new technologies. That means less  time for air-to-air combat training. The justification is that U.S. equipment, and overall pilot skill, still gives American aircraft an edge in any likely air-to-air combat situations. Meanwhile, there's a war on, and pilots need to be ready to do what needs to be done right now.