Compared to humans, chimpanzees have a tall and narrow pelvis, flat feet (not arched) and a differently shaped backbone. In short, a chimp’s skeletal structure is ideal for quadrupedal locomotion and when they are on the ground, they generally use all four limbs to get from one place to another.
This is not to say the chimps don’t use just their legs sometimes. It just looks like it takes a bit more effort:
But sometimes it can be convenient to switch to bipedalism:
The chimps have incredibly strong upper bodies that are perfect for climbing and swinging.
And having opposable toes comes in handy to add that bit of extra grip when you need it.
Sometimes, when they are feeling extra daring, those toes are all they need:
