What's the real reason the Navy and Air Force tends to shun former Army and Marine personnel from joining their branches?

SSgt Robert Jorgensen - I'm amused by your answer. I like it. But if I were young enough to consider being able to reenlist, or were I eligible even with a med retire, Any AF or Navy recruiter who walked away after finding out I was "subpar" would get a quick call to their back saying, "Did you know I had a 121 GT?" I found plenty of grunts in the military who had smarts, but didn't want to be tied to a boring MOS, they wanted to be where the action was. Back when I was a PFC stuck in the TOC as a radioman, I was told by JTAC's that (at that time) the only MOS the AF would accept for that particular AF MOS was Infantry. They knew most Infantry could hump the load that JTAC's were required to carry without much complaint.
TSgt (Join to see) You should be looped in on this answer here. Truth is, I've known quite a few "dumb grunts who only know where to fire where told" that could do just about any job in the military they set their minds to.

Never knew me then did ya!

The last year I spent in the Navy as a Hospital Corpsman, we had a prior service (USAF) guy transfer in. He was the USAF version of a medic and frankly, one of the smartest, and very squared-away Hospital Corpsman I ever came across. He came into the Navy as a PO2 (E-5) and was highly skilled.

SGT Jim Wiseman - Roger that! That's why I said I liked your answer. I didn't show it in my response, but I caught the sarcasm. The interservice rivalries, but with good spirits. I give crap to Marines, but let an AF or Navy guy try giving either Army or Marines crap, they get side-eye.

SGT William Fisher -
"Right, because Heaven forbid the Zoomies should actually try and act like a professional military force. LOL"
WOW!..THAT'S a pretty broad 'brush stroke' you're painting there...Fisher.
And...as I mentioned to another prior poster...judging from your posted photo, you were either VERY young...OR...NOT even BORN yet during MY USAF active duty time...12/1964-10/1967 stateside..10/1967-10/1968 in S.E. Asia, then my DD-214.
TRUST ME, when I say...during MY time IN!..at least MY squadrons and those I WORKED with and rigged...WERE...PROFESSIONAL!
Working in the 538 section...we rigged MOST any aircraft...F-4 Phantoms, T-28's, Air America, C-124's Globemasters (aka Shakeys), 130's and 141's (C-5's and 17's didn't EXIST yet), the HH-43's and 53's with the 38th and 40th ARRS (Air Rescue and Recovery Service), and many TDY's.
So YEAH...you get the idea...we WERE professional!

My Father was retired USAF and a Chief. He said the same thing. He was dismayed by the way the Air Force has gone to be a more corporate branch. He said till the day he died the worst thing the Air Force did is forget it Army roots.

Their mission is different, their support is different, as well as their subculture. So, do not expect to get into their branches and impose you gun-ho aptitude. Know your environment! and you will succeed

SMSgt Lawrence McCarter - As an MP during different years at Walter Reed, and Ft. Belvoir, VA ... we had occasion to go to Andrews AFB. Honestly, as NCO's we were totally impressed with the Air Police as I think they were called then. Super sharp in khakis, badges, leather gear with revolvers and low quarter shoes. At the time, we were still blousing our boots and in khakis or dress greens, wore the MP Brassard (armband) and .45's. The only thing I thought the USAF AP's were lacking, was the .45 vs their .38's.
Now, it seems that all service branches law enforcment folks wear the cammo crap which, to me, is the most unprofessional uniform there is - for law enforcement duty! Everytime I see Army or Marine MP's, the look like they slept in the cammies. I exaggerate but they do remind me of pajamas!!!!

SGM Dawson, you sound like my brother who went into the Army from 1954-1957. At one point he was stationed in Germany and went to a AF base for a few days. He told me while he was there he slept on clean white sheets, and when he went to the mess hall the line cook asked him how he wanted his eggs cooked and what kind of meat he wanted. When he got out he came home and told me don't go into the army, go into the AF, you get treated better. I took him up on that.

In 1974, while stationed in Japan, I had to go to Yokosuka Navy Base for a couple of days. and I thought I would just stay there instead of driving back to Yokota AB, which was about 20/25 miles away. It would have taken me about two hours to drive because of such heavy traffic. When I went to billeting they sent me to a large warehouse that had all these bunks stacked I don't know how high. The bunk that I was supposed to have was so high I couldn't see it from the floor. Needless to say, I decided to say, I drove that two hours back to my base. I was a E-6 at the time, and if someone the same rank came to an AF base, they wouldn't have been treated the same.
On another occasion I was a First Sergeant and one day I was performing room inspections in Billeting with a Master Chief. In one of the rooms I had a E-6 temporary sharing a room with a E-3. The Master Chief said that wouldn't happen on a Navy base and I asked him what would he have done. He told me the E-3 was have to stay in a pup tent. I told him that is why the AF has better retention then the Navy does. That E-6 was married and drew housing allowance. He was just waiting for his family to arrive so he could get base housing. So really he shouldn't have been in the room in the first place.

Blood! Blood!! Bright red blood!!!

I was active-duty Army when my child became a high school junior. I'd been stationed in Korea with Air Force personnel previously. I did not let any Army recruiters talk to my children at all. I knew how I was treated even as a senior NCO, and I did not want my kids treated that way. My advice to them: go Air Force and you will likely have a masters degree when you retire. Added bonus, 1) no KP duties ever, 2) wooden furniture like real human beings, 3) mess hall buffet or line-cook choices, 4) no open bay showers filled with soap scum, 5) wont to carry dirty food trays and dishes to the mess kitchen because you are valued.

Col Jonathan Brazee - As a Hospital Corpsman in Nam, we LOVED Army chopper pilots. We (mistakenly) viewed them as having bigger nads until we realized their Medevac Hueys were the newer and FASTER birds than the Corps which was typical in most equipment issues.