Why are Airmen overlooked for the Medal of Honor?

I think that by the very nature of the USAF, the possibilities for an action worthy of the MoH are limited. Back during the Viet Nam war, particularly on airbase defense, there were many airmen who's actions most likely merited consideration. Especially during the Tet Offensive in 1968. I have heard of and read of exploits of Security Policemen who went "above and beyond" in defense of their bases. Now the USAF Spec/Ops airmen may be involved in activities that would merit the highest award for valor.

They aren't, several crewmen have been recipients, but I have never seen an entire crew get one- which is what it would normally take for airmen.

Most AF jobs are not direct combat mos, so it's going to be tilted to Army Marine Corps. but there are AF MOH winners.

It may be my faulty memory, but I believe a para-rescue man received one in Viet Nam. That's part of the helicopter crew (Jolly Green Giants) that are sent to rescue downed aircraft, and other rescue efforts. I also recall a facility or street was named after him. Other than that, there are not many AFSCs where airmen were that near to the front lines, until the current uses of them with transporting supplies, forward observers, etc. Most of the USAF closer contact with the enemies were pilots.

Two recent MOH winners were a Soldier and a Marine who earned it in the same battle. not sure if they were recommended by their respective services or one or the other

Because the Air Force personnel are seldom placed in a position to earn it due to having very few ground combat positions, unlike the Army and Marines. Most of the Navy personnel that win it are SEALS.

I would say the number of Battlefield Airmen verse the number of Soldiers and Marines on the ground have a lot to do with the reason. In the Air Force you 6 specialty codes comprising 4,099 positions: 13C special tactics officers, 13D combat rescue officers, 1C2XX combat controllers, 1C4XX tactical air control party (TACP) airmen, 1T2XX pararescuemen, and 1W0X2 special operations weather enlisted airmen. And when you look at those numbers, reality is that is what a third of those positions deployed at any one a time (this is a straight up guess). Reality is just the AF does not have the large number of Airmen put in those situations where a Medal of Honor is warranted. In a lot of these major battles where the MOH has been awarded since 9/11, there were one or two AF airmen there, and in other cases, there were none.

Is John Levitow the only Airman to ever receive MOH?

I know of one AF Captain awarded the MOH because of where I moved. https://en.wikipedia.org/wiki/Hilliard_A._Wilbanks