When has the last B-52 been shot out of the sky by a belligerent, any one, Bueller, Bueller...
The snarky answer would be 31 B-52s lost in Vietnam.
The straight/serious answer to a fellow FReeper is because the B-52H is a woefully obsolete aircraft that is only viable against low-technology adversaries that do not have a cogent air defense network. Against such an adversary, the B-52H is an amazing bomb truck that, with JDAM technology, is akin to fire from heaven as far as Jihadis are concerned. However, against an adversary with an advanced integrated air defense system (IADS) the BUFF is simply a big, slow, helpless flying target.
People don't like to hear this, but the same applies to the A-10. Yes, it has a 'titanium bathtub,' and yes, it has a big @$$ cannon, but it requires sanitized airspace to operate in. Put it against an adversary that can actually fight back and, armor or not, A-10s are done. (During the Cold War the joke among A-10 and Apache pilots was which would suffer the most if the Soviets ever came through the Fulda Gap).
Anyway, while all of the US' adversaries in the last four plus decades have not been strong (the likes of Somalia, Iraq, Grenada, Bosnia, Panama, Libya, Afghanistan), and thus a B52 would work well there, there is always the chance that the US may operate against the likes of China or Russia. BUFFs, for all their myriad advantages (and they are a strong workhorse, together with the B-1 Bone), would be dead.
Could the same ultimately be said for the platforms of the Russians and the Chinese. Can they mount an adequate attack structure to gain air superiority over the U.S. in most theaters? If so how long could they hold it and could hundreds or thousands of unmanned armed aircraft offer so much resistance that we could overwhelm them.
Like I said I am not a military person. I never served & do not even read Jane’s.