Why are there two sets of the Ctrl, Alt, and Shift modifier keys on the keyboard?

Why are there two sets of the Ctrl, Alt, and Shift modifier keys when only one of each is necessary?

Solution:

When touch-typing, you use the alternate side “function” keys.

E.g.

qwer,asdf,zxcv you’d use the right shift with your right hand without needing to stretch your left hand while pressing one of the aforementioned keys.