Beam 2 has a larger second moment of area (I). By placing more material far from the neutral axis, the flanges make a large contribution to (I=\int y^2 dA), so the same bending moment produces lower curvature and lower bending stress.

Beam 2 has a higher centroid, so the neutral axis is further from the applied load.

The web of Beam 2 removes material near the neutral axis, where bending stress is highest, directly reducing the maximum bending stress.

Beam 2 has more total area, so there is more material to resist the bending load.

Beam 2 distributes bending stress uniformly across the cross-section, so the peak stress is reduced.