Why is it that two areas of the earth with the same latitude have very different average temperatures?
This is because latitude is only part of what determines a climate. Other factors such as elevation, wind currents and nearby areas of water tend to be most significant in determining climate. For example, since California is bordering the Pacific Ocean, it’s climate will be a whole lot different than somewhere in Oklahoma of the same latitude (and both of those will be different than somewhere in the North Carolina mountains at the same latitude).