For the same reason, the DC-3 is still flying: Damned good design. I once worked near Wichita Fllls, TX, Every day going to work I would drive past the B-52s lined up on the runway at Shepard AFB. Man what power they exuded. And the men flying them were the elite of the USAF.
Back in the mid 60s, I worked at Ellsworth AFB in South Dakota. One of our jobs was located next to the runway fence. To see those 52s doing touch and goes was awe inspiring. The power as they accelerated (at a seemingly impossible angle) was chill producing.