Mainly it's relatively low operating cost compared to modern bombers. Also it's readiness ratio is much higher than anything more modern (75% for B-52 vs 50% for the B-2 Stealth Bomber).
I'm not sure how retrofitting bomb doors (plus any other military requirements) onto a modern wide-body Boeing would be any better than a major refit of an existing B-52. Heck, we can't even build new tankers for in-flight refueling without major fuckups and overruns. A bomber would be worse.
Oh I'm sure I'm wrong and there are good reasons... but it's just hard to quantify them exactly.
The speed/"B52 is actually structurally designed to take enemy fire" points someone mentioned were immensely informative.
I'd never, ever thought of those. But it makes sense. The B52 carries a lot of bombs and has the structural design and other attributes for being in a combat zone.
Designing a NEW B52 is prohibitive because in reality, in a war with Russia/China, the B52 is non-viable against modern AA.
But for carpet bombing Afghanistan, the B52 is perfect.
I'm not sure how retrofitting bomb doors (plus any other military requirements) onto a modern wide-body Boeing would be any better than a major refit of an existing B-52. Heck, we can't even build new tankers for in-flight refueling without major fuckups and overruns. A bomber would be worse.