Ozone is heavier than air, so it would just cover the ground and poison a lot of people. The reason the ozone layer doesn’t fall down is that the ozone in the ozone layer is actually constantly being destroyed and formed anew from oxygen under ultraviolet sunlight. At lower altitudes there’s not enough ultraviolet light to produce enough ozone to match the rate at which it would be destroyed again.

also, ozone concentration is highest in the upper stratosphere, which is over 150,000 feet in altitude, whereas most commercial airplanes fly at about 35,000 to 40,000 feet