Why don't all members of the Air Force have to be fully qualified to be a rifleman in case of hostile events?

Because some dumbass in SAC Headquarters convinced other dumbasses that they coud save money by not arming all military personnel assigned to the bases. SAC was the leader in this idea.

My leadership class project addressed this exact issue back in the 90's. Although our fellow Reservists were supposed to qualify every three years, the average maintenance airman had not done so for eight. Although they individually felt confidence in their own abilities, several expressed more concern about fellow troopers than a potential enemy.
Although airmen aren't expected to withstand a protracted siege, we should at least be able to "hold the fort until the cavalry arrives".

Is this a new thing that other specialties are not being trained to use a weapon? When I was in there were times that I was at the range teaching others how to use different types of weapons. I also was security/ law enforcement forces. I spent a lot of time on the range because of the number of weapons that I was qualified on so I was training others on techniques of cleaning and stripping it down to put it back together. If they have stopped this then they have made a mistake it is good for all members to know how to handle a weapon.

When in doubt give your ammo to a MARINE. Better yet, reload his mags for him.

I was in the Secuirty Police in the late 70's, early 80's and think most people join the Air Force more for the technical aspects of the job rather than being a fighter. The majority would rather leave that up to those of us in the Security Forces since that is our specialty. But I do agree that everyone should be required to qualify each year with basic weapons just in case.

I was in communications. Let's concentrate on the job we were trained in.

When I was in the 82nd. I learned formations and how to leap, cover and scan. I took a group of medics and pushed back a smaller group of rangers who where picking off my unit one by one during a training exercise. My 1st Sgt was clueless to what I was doing and open fired on me and disrupted my attempt to push the invasion out of the compound perimeter. They left anyways. Another time I took two other medics and captured a ranger by out flanking him. He was surprised that I knew how to do these maneuvers.
I grew up in the Country and played war with my brother. We watched war shows all the time. I listened to WWII, Korean and Vietnam Vet stories. They told me what happened, the mistakes that where made. I played strategy games.
I could hit every target spot on up to 250 yards because I could see the bullet hit or miss the target. Now at 300 yards I could not see it because it was to far away. They test my vision to be at least 20/10, they told me that they did not test people anymore than that unless they where going to be pilots.
When I went in to qualify I hit every target never missed until I did the burst where I actually only hit 3 out of 9. The M-4 is so easy to use compared to the M-16 it is amazing. The scope was incredible compared to having to qualify with the old iron sites. Yet as a Nurse they let me pass because I had a perfect score before the burst. I was the best marksman in the class. In the 82nd when I went through we never fired burst at a target to hit it. That was a new concept. Burst was just fired for fun and for effect. We could see that when burst was fired that the weapon pulled up. Yet we never learned or where taught how to adjust for that like they do now.
My Doc and my RT where poor shots and told me that they would be better at hitting someone if they threw the weapon at the person than actually fired the weapon. I told them just let me do the shooting then if we ever had to do so.
I am glad I went into the 82nd because they taught everyone tactics because we where all first and foremost combat infantrymen then I was a medic. Even though I told myself I was a medic first. They treated us as infantrymen for the most part. We did security, we dug and layed in fox holes. Set up concertina wire.
In the Air Force I learned almost nothing. When I brought up security concerns, as I was taught in the 82nd to do. I was told to keep my mouth shut because I was only a nurse and they laughed at me. twice until the rockets where landing and people lives where at risk the first time and the second time when they found explosives in a bunker right before an attack. Yes, the Air Force has a lot to learn. Everyone, is part of the security team and should be listen too and trained. No, one should be blown off even if they are just a nurse, they might just have been an Army 82nd Airborne paratrooper who did security before they became a nurse!
I feel your frustration and I know lives have been lost because people are not trained and we don't do the right thing which could have saved us lives and money. Yet we waste money in other areas! I have seen people die after information was given that could have saved them by me and other officers who had prior experience (Prior Special Forces, Engineers and so on) Yet we where told by members of Congress that, things where handled and the people at the pentagon knew better than the people on the ground.
After several people died and a few months went by they did some patches, and took a few of our recommendations into consideration. Always to little to late. They let people die and spent millions doing nothing. Same old thing. It still bothers me and I think it will the rest of my life but what else could we have done when no one else would do anything even all the way at the top (Congress and White House)! God bless all who died and forgive the people who could have saved them. I tried and many others did the same, good officers who cared but where just beaten down.
The system never changes.

I just recently finished doing a firing course with Navy MPs around 120 to be exact. They could not hit the broadside of the barn. It took most of them around 10 mags worth of ammo to zero their targets. Even when we went to the qualifing range they still couldn't hit anything. The Army ended up almost running completely out of ammo on the range.

When did that requirement get dropped for Air Force personnel? We had to qualify out of Basic or we didn't leave Basic. Then we had to qualify every year and before every deployment overseas. I was in the last flight to qualify on the M-1 Carbine out of Basic. The silly thing actually rattled if you had the temerity to shake it!

As a flying buff crew chief I was m-16 and m-9 and 38 qualified. I thought of it as a good thing. However, I truly don't believe I would trust some people with a weapon of any sort, including a butter knife! I believe it was a Japanese officer who stated something to the effect of if they were to invade the Continental 48 they would be fighting a war they could not win, because if the fact of at that point the civilian population would blow them to hell.