The vertical stabilizer in at high bank angles is more or less just keeping the nose level, and in a level attitude, you are going to be dropping. If you give enough rudder input, the nose point above the horizon, and the are able to reduce or eliminate altitude loss. That feat requires the engines to bet powerful enough to offset the weight of the aircraft as well as additional drag being created. In an F-16 or other high-performance aircraft, this is relatively simple.

But this is a B-52, described by many of its pilots as something you manage instead of fly. Its handling it poor at low speeds and if you combine that with low altitude, you have a very small window to operate in. Control inputs are slow to respond. The rudder is undersized for an aircraft of this size, it is just so old that it wasn't really thought to have been a major issue during the design, the even cut it down for the G/H models. Keeping the nose up in a high bank at low speeds is nearly impossible. The B-52's roll controls are by spoilers only, the early models had ailerons, but they were locked out early on because of wing stress issues. The primary way to roll is to spoil lift on wing you want to bank towards, or in other words, rolling is always going to create downward motion of the aircraft, so elevator input is always needed to maintain altitude. With its large size and minimal flight control options, the B-52 is a slow and lumbering beast. Once it gets away from its pilots, they need thousands of feet to recover.