1) Roosters don't provide eggs
2) Roosters tend to fight and cause other trouble
3) Roosters crow
4) Feeding and housing roosters can be expensive.
In very rare cases, there are farms that do allow roosters to live. One farmer detailed his success at letting roosters live, though the roosters would fight each other in order to try and mate with the hens. As a result, he separated the roosters from the hens, and was surprised that this put an end to their fighting and competing (Link). Other forums have detailed similar success stories (Link). So, as long as a farmer is willing to deal with the crowing and the extra money for feeding and housing roosters, it's evident that roosters lives can also be spared.
Another possible option is to allow roosters to live in the wild. Chickens can actually thrive in warm or tropical climates, as evidenced in this video: