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

I wasn't in the Air Force, so I'm not familiar with what they get trained on. I always figured that they had some weapons training. I can see where they might not need to qualify on m16. I do think everyone in the military should have some weapons training because it helps enforce the seriousness of the business. A lot of the of soldiers first time to ever touch a weapon is in Basic Training. I think the training could be a very good thing.

I was familiar with shooting as a kid before I joined the AF in 1956, so I promptly fell in love with the M-1 carbine, their weapon at the time. It made a polite little bang, with no recoil at all, unlike my deer rifle "Ol' Kick an' Beller".
With today's weapons, it shouldn't take any more than a couple of day's instruction to determine which end the bullet comes out of and hit a target with it. I don't think that's asking too much out of a basic training schedule. After all, don't all youngsters think they're John Wayne? Or Juanita, as the case may be?

Excellent point; especially on you rhetorical question, "ummmm why did you join the military in the first place ...?"
Being a prior crew-chief, I was well aware that a perimeter breach left is with a very short time (I think it was a matter of less than a minute) before any of us expired. Using a small tool box for cover with out the ability to return fire successfully would only serve to enhance the shooters position. That is, of course, if the airman could find the safety in the first place.
The AF doesn't necessarily need to know battle tactics, but should know how to defend themselves should the Army or Marines ability to defend the base's perimeter to full extent be comprimised.
It's happened.
If aircraft don't launch, ground pounders will be at a disadvantage. That and the enemy has our equipment. Correct me if I'm wrong, but- sans rules of engatement - in a nutshell that's all there is to it.

If you are a part of any branch of the military you should know basic Rifleman

All Air Force members, while at Basic training received weapons qualification. At least when I entered the military, that’s the way it was.

I'm About Six Years Older Than Dirt, Served From 61 - 65,
But I Think We All Had To Be Range Qualified Before Basic Training Ended,
Have The Rules Changed?

In regards to modern USAF personnel, recruiting measures are leaning away from actually being "military" and more just a career. As far as training everyone to be on par with basic marksmanship, too far of an unacceptable attrition rate would be incurred with mandate marksmanship for all positions in compliance with the recruiting measures. I absolutely do not agree with it from a personal opinion. Now if it were to come down to the budget comparison, if you don't have a service branch than can fully defend itself, then you do not have a military service branch, you have entry level cub scouts. I do note that specified jobs require it and I tip my hat to the fact. I am repulsed by the lack of self preservation capabilites on a mass with far too many individuals in this country and in the "military" today. Forget the fact I'm a Marine. I do my best to know history. Hardship creates strong citizens, strong citizens create good times, good times create weak people, weak people create hardship. Sic vis pacem, para bellum!

Let me preface my comments with I am prior service Army (12 yrs Active, with the 82nd Airborne Division) and I joined the Air Force Reserver after a 13 year break. I completely agree with your assessment about everyone needing to be prepared. What I cant believe is that in most deployed environments the Air Force keeps all weapons locked up in an armory (unless your in a forward location), the only ones carrying daily are SF. So to your question about what are we supposed to - well the answer is die when an attack comes - because by the time we get to the armory to draw a weapon its gonna be over, and not meaning any disrespect but SF is not infantry and against an elite unit that might specialize in Air Field seizure or rear area disruption like special forces types of units, you do not have the man power or quite frankly the skill set to fight them off. You dont train for those types of scenarios in earnest, because we have units that specialize in these areas you can rest assured that our enemies do too - we should train against units like the 82nd Airborne division or Rangers in large scale air field assault exercises so we can be prepared for the reality of fighting against these types of scenarios. Then on to the weapons skills, the Air Force is only required to fire once every three years, as you are aware shooting is a perishable skill, if not continuously reiterated its gone. The time between shooting is enough to become forgetful and nervous enough to not be mindful of what they are doing. Not all of us have our own AR weapons to stay proficient with. Maybe when something like this happens leadership will rethink how this is done.

I am a retired Air Force officer who qualified on the M16 before going to Vietnam and was qualified on the .38 pistol most of my years in service. For most of us this level of familiarity is adequate for our everyday duties, which could include flightline maintenance, civil engineering or any other of a range of support activities. Aircrew members had different qualification requirements as could other service members whose exposure to combat might be different from everyday duties. Full qualification as riflemen would demand regular training which would be expensive and would require considerable time away from regular duties, with relatively little value in normal operations in return. I agree that some ground combat training is valuable to any military culture, and a higher level of training could be justified--however training airmen to be ground fighters could very well be a waste of resources. We should always prepare for our primary missions and be prepared to execute them fully, which we do well by and large. I have always been grateful to our sister services for their contribution to national security. We also contribute to national security and do it quite well. All of us could always do better and we should try to do more as we are able.

CONOPS. For the vast majority of AF they don't expect to places bases/troops anywhere near frontlines where such a threat exists. The threat to such bases are from acft/missle attack and no small arms can defeat theres. So it becomes a cost/benefit analysis. Why spend a pile of $ to defend against a threat that will not be encountered?