In this ASE answer What is the maximum safe bank angle of a 747?, the author writes:
If we stay with stationary turns (without the "falling out of the sky" part), the maximum bank angle is given by the maximum load factor of the 747. At 400 KEAS, this is just 1.5g, so even with the 25° nose down attitude the maximum bank angle would be 53°. If you fly slightly slower, the load factor goes to 2g (equals 63° in a 25° descent) and tops out at 2.5g at 310 KEAS (68.7° in a 25° descent).
Why does the allowable load factor vary with KEAS in this aircraft?
Note that if the wings have any washout, the outboard portions of the wingspan would contribute less to any given total lift force at higher airspeed (lower angle-of-attack) than at lower airspeed (higher angle-of-attack), so for any given G-load, the higher-airspeed situation would seem to impose less upward bending moment on the wing structure.
Is it simply that imposing a drag load makes the wing less capable of absorbing the lifting load?