I remember a video with B17s in WW2 that didn't carry bombs but had like a triple load of guns and ammo. And it seems like the idea would only get more effective with long range missiles. I get it's not much of an issue these days when our most frequent enemies don't really have a meaningful air defense capability but the story was different in the Cold war and and Vietnam. I picture:
B52 "Wild Weasel Plus": It's much like any other B52 but this one partnered with AWACS, had a few dozen vertical launch tubes for an assortment of Standard, Phoenix and Sparrow missiles. In place of its rear facing quad fifties was a "torpedo room" where the gunner would stuff Stinger missiles into tubes. Out on the wings, in addition to the cruise missiles the existent ones carry it would have a mix of anti radiation missiles. The weight of radars and munitions could not have been more than the bombs it would normally carry. Everyone in the 60s-now thought dog-fighting was over anyhow. Fighters didn't have the range. So what gives?
C130, 747 or something else fat and slow with a "Defense Package": Basically the torpedo room from above. Soldiers carry Stingers on their back. Why not give big vulnerable planes some bite?
Um. You cant launch a "surface to air missile" SAM, from the air, because then it's an air to air missile. SSBN's carry ballistic and cruise missiles, the latter of which our heavy bombers do as well
Furthermore, chaff, flares, and radar jamming, along with the "wild weasel" missioned aircraft, are pretty effective.
"Air mobile SAM sites", discounting the terminology mix-up (they'd be air-to-air missiles, not surface-to-air) are essentially fighters. The problem might have had something to do with the fact that during WWII, the bomber formations, even those with gunships, got cut to pieces without their fighters. Fortunately, the Pentagon in its infinite wisdom developed and built tanker aircraft for the fighters (and bombers) to use on their missions during the Cold War, negating the range issue for the most part.
As a final note, remember that missiles can only turn so much in their flight path. A B-52 carrying them would have to turn in three dimensions in order to aim and launch missiles throughout most of the Cold War, due to the limitations of aiming technology. Otherwise you have to have "launch tubes" everywhere a B-17 had guns. Not really a feasible option when you're dealing with rocket exhaust. (The alternative to that is a catapult system. See: USS Enterprise, length of.)
Huge issues with the terminology as others have pointed out. SAM, SSBN, Standard, Phoenix and Sparrow missiles, Stingers.
You're basically asking why we didn't equip bombers with anti-aircraft missiles.
Because bombers are offensive aircraft that hit ground targets. Fighters are the defensive aircraft that shoot down enemy aircraft.
Basically, fighters were already equipped with missiles. As for the claim that fighters don't have the range, they have external fuel tanks and aerial refueling as well as airbases located closer to the front.
It has been done - at least once. During the 1982 Falkland's war the British armed some Nimrod aircraft with Sidewinders. That event is used as justification to expand on the practice in the book - The New Maginot Line. The fact that it is not done according to the book is due to a conspiracy of sorts by the defence industry who the book asserts wish to make as much money as possible - who would naturally reject the idea in favour of making specialized aircraft (fighters) to carry such weapons.
Your assertion that bombers are big vulnerable aircraft has merit. Therefor it is far better to not risk them - to not fly them into such peril in the first place. The days of bombers bashing their way through dense flak and SAM belts to fight their way to the target are well and truly over with the advent of stand off weaponry. So your original contention is kind of irrelevant.