I thought Beef was a pretty funny character. His demise is one of my favorite movie scenes. I saw the movie (over and over again) when I was in the Army. The base theater was one of the few sources of entertainment at lovely Ft. Dix, NJ.
My guess is that the airframes are in short supply. At least half of all P-39s produced were given to the Soviet Union via lend/lease. Many of the types that are currently raced (P-51, F8F, Sea Fury) were built in much larger numbers or post war.
I owned one back in the early 1970s. It was kind of a dog and broke timing chains distressingly often. My mother sold it for a pittance when I went into the Army. Oh wait, you were looking for inspiration.
Update: The car that I owned was not a Ram Air, it had the base 400. I noticed that your kit is a Ram Air after I posted.
Don't dismiss the P-39 Airacobra. A P-39 with an engine out of a P-63 Kingcobra won the 1st post WWII National Air Race Thompson Trophy. Although a pre WWII design, the P-39 was fast and highly maneuverable at low altitude (where most air racing takes place). The P-39 also features a unique mid-engine layout. Good P-39 kits in all of the major aircraft modeling scales are as common as dirt.
No. 14 1958 Sebring winner Hill/Collins
No. 14 1958 Le Mans winner Hill/Gendebien
(most likely the decals are for the Le Mans car, because, as you stated, the Sebring car was RHD)
No. 102 1958 Targa Florio 3rd place Hawthorn/Von Trips
No. 12 1958 Nurburgring 10th place Kochert/Bauer
(Bauer was killed at this race and in this car, when, not realizing he had taken the checkered flag, raced on and crashed, later dying from his injuries.)
Why? Perhaps various obsessive/compulsive disorders, more money than time, more money than skill, easier to buy than build, eyes bigger than stomach, etc. The next generation of model builders should have a huge selection of unbuilt kits at rock bottom prices to choose from.