Amperage Higher Than Device Why Don't The Switches In A Breaker Box All Have The Same Amperage?

Why don't the switches in a breaker box all have the same amperage? - amperage higher than device

Why is the dryer, spacious, and a central kitchen and the use of the drive amplifier circuit C 40-60, but all rooms with 15 amp circuits? Electricians always seem high intensity circuits exclusively on kitchen appliances and dryer. Is there a special reason for the beach, Hair and A / C amplifier circuits are higher, but use the parts and lighting to a 15 amp circuit? And if all programs use the same amperage of 15 amps? Dangerous?