The engine is part of the chassis

In a road car the engine sits in a frame. In F1 the engine IS the frame: the monocoque bolts to the front of the V6, the gearbox bolts to the back of it, and the rear suspension bolts to the gearbox. Remove the power unit and the car falls in half. That means the engine block isn't just fighting combustion pressures — it's carrying suspension loads, aerodynamic loads, and crash loads, all while its internals spin at over 10,000 rpm.