Why do people call roosters living alarm clocks?

The ancestors of domestic chickens are all birds. Every breeding season, males will show off their courtship to females with their bright feathers and songs. Roosters are no exception. They also show off their courtship to females with beautiful feathers and loud cries so that they can mate and pass on their offspring. From this point of view, the crowing of roosters is definitely not to announce the dawn to other creatures (including humans), but their ancestors went out for food long before dawn.