Its much more simpler than many realize: $$$.
The P-47 WAS dreamed about by the pilots in Korea who were NOT happy with the fragility of their liquid-cooled P-51s which were escort fighters and were in no way effective fighter bombers holding only six .50s to the P-47’s eight, 1880 rds of ammo to the P-47s 3200 rds, and only 1000 lbs or ordnance to the P-47’s 3000 bombs of bombs AND 10 5″ HVAR rockets. Mathematically it took three P-51s to carry the ordnance of one P-47. And the long-range P-47N model actually had a further range than the P-51D of 2350 miles to the 51’s 1650 miles so that wasn’t a problem, either.
Or as Ed Schmued, THE chief designer of the P-51 for North American put it about P-51-s in Korea:
“335 F-51D Mustangs were lost in the Korean War, with 264 pilots killed or missing. Of these losses, 172 fell to enemy ground fire, ten to enemy jet fighters, with forty-four missing and unaccounted for, and the remainder to accidents. Ed Schmued: “Unfortunately, the P-51 was a high-altitude fighter. [In Korea] it was used in ground support work, which is absolutely hopeless, because a .30-caliber bullet can rip a hole in the radiator and you fly two more minutes before your engine freezes up. Flying a P-51 in ground support was almost a suicide mission. It is unfortunate that the airplane had been used for ground support, but in the Korean conflict we were short of airplanes and anything had to do. This was the reason for using the P-51 in low-level operations.”
The survival rate per combat sortie of the P-47 was 0.7%, best of any fighter in WWII. The P-51’s was almost twice as poor at 1.2%. (Numbers from “American Combat Planes” by Air Force Historian Ray Wagner.)
One of the main reasons for going with the P-51s after WWII was because of a serious lack of P-47 spare parts. The P-47s had been fighting harder (in the skies and on the deck in the ground attack role,) longer by a full year as they became operational a year before the P-51 and the P-47 fleet was battered and weary and her parts stores were almost depleted.
Another significant issue for an almost broke Air Force after WWII was the price: $83,000 for a single, very complex P-47 with a turbo-supercharger, and many options a P-51 simple couldn’t offer to $51,000 for a bargain-basement P-51-you could buy three Mustangs for the price of two Thunderbolts.
Another issue was the smaller size of the P-51 allowed more to be transported on carriers and transports to get them over seas.
There is no doubt the P-47’s would have been more survivable to ground attack pilots in Korea and the pilots knew it and were embittered about it, the same as the P-47 performed in WWII but the logistics simply weren’t there-it would have been too expensive to bring the P-47 to Korea.