Ah, the good old days of construction are still alive in Mexico!
Some 35 years ago I learned bending rebar by hand too.
We also learned to calculate the length of the initial piece of rebar needed to achieve the end product, since steel gets longer by bending it five times, so you wouldn´t waste any steel.
I forgot all about it, I just remember it has to do with the radius of the round metal piece one is bending the steel around, the bigger the radius the longer the steel gets, and the thicker the steel the bigger the radius needs to be.
But on the construction sites we usually had rebar pieces which were bent by a machine, we just had to tie the stuff together with wire by hand.
We only had to bend rebar by hand if a piece was missing and it was faster to do it ourselves than to order it.