[missedthecue]

Then why do four legged animals still exist? Especially animals that walk a lot. Elk, wolves, etc...

[monocasa]

They can reach higher top speeds.

[sharatvir]

Could be misremembering but I recall reading that bipedalism in humans correlates with a narrowing of the birth canal, potentially increasing mortality during childbirth and also selecting for infants that are underdeveloped compared to other newborn mammals.