The reason a rooster is made into a capon has mostly to do with the quality of the meat. But also, a capon is less aggressive than a rooster and is easier to handle.
Capon meat is tender and flavorful, compared with rooster meat, which can be quite gamy. Capon meat is also relatively fatty, and has a high proportion of white meat. The difference between capon meat and rooster meat is due to the absence of sexual hormones.
The process of making a rooster into a capon is called caponization. A capon is usually castrated at around 8 weeks of age or earlier. Capons are generally slaughtered at around 10 months of age or younger.