Why is a castrated bull called a steer?

Often the bull that is being castrated isn't suitable for breeding purposes because of lack of adequate structural conformation including small testicles, bad legs, too much femininity, too shallow in the gut and heart girth, bad topline, etc. Bulls that lack libido are also cut. Other reasons could be that there are too many intact males in a herd that young bulls don't need to be used in that breeding herd and are banded. Bulls that have inferior genetics due to the history of their dam or sire or their overall performance are also cut.

Steers are more docile and less dangerous and unpredictable than bulls are. They also bring a premium to the North American market, and marble better than bulls do. Steers are the main animals found in feedlots that are fattened up for the meat market, since the demand for meat from steers from consumers is so high.