Video of B-52’s taking off (cued to 1:35).. Notice that the nose barely rotates upward before the plane lifts off of the runway.
Video of 747 taking off (cued to 1:53). This is pretty representative of commercial airliners in general: the nose of the plane pitches up 10-15 degrees before the plane lifts off of the runway.
Why the difference? Are these B-52’s carrying no payload (and 30 minutes of fuel)? Are they using way more runway (and reaching a far higher takeoff speed) than they really need? The B-52’s takeoff behavior is more in line with that of the U-2. I’m not surprised that the U-2 does this, since it’s designed for slow flight in extremely thin air. But why would the B-52 behave like this?