That would also require fatter wheels. Which together have higher moment of inertia which makes for slower bikes (as more energy is required to get the wheels to the same speed).
I could be wrong, but it turns out that somewhat fatter tires with lower pressure are faster because less energy is wasted by deforming slightly and rolling over small bumps, as opposed to thin high-pressure tire "bouncing" over pavement. There is less wasted vertical motion with the wider tires.
Not exactly what people want in a race.