One chooses different leg designs for different reasons. Sometimes there are specific design goals, involving the workspace, manipulability, and dynamics, but sometimes the designs are less intentional, with choices made for other reasons.
Petman, the predecessor to the Atlas series was designed to mimic human kinematics for testing protective clothing. The iCub series were also specifically mimicking humans rather than designed to a performance spec, and the first generation of those could not walk.
Hurst (the lead person behind Cassie which is the robot you pictured) switched from his previous approach (Atrius) to the bird approach after collaborating with people that studied bird walking.