Is the plastic body of Canon 60D poor? Is the metal fuselage that important?

Canon's 60D is engineering plastic+glass fiber, which is stronger than plastic and lighter than metal. Moreover, suddenly entering a warm room after shooting in a cold place, the condensation phenomenon and negative effects are smaller than those of metal. The bayonet part is metal to ensure strength. In this day and age, unless you want to smash walnuts with a camera, you should choose something light and easy to carry on the premise of the same image quality. 30d, 40d and 50d are all metal bodies, while 350d, 400d, 450d, 500d, 550d, 600d, 1 100d and 1000d are all plastic bodies, as long as the main components are durable. Why does the body need so much metal?