Why are helium and the free hydrogen very rare on earth?

Too light and too close to the 1/6 rule in escape speed from earth's gravity. A gas must be withing 1/6 of the escape speed from earth's escape speed for it's gravity to be easily retained in the earth's atmosphere. These two gases are heated too easily. are too light and too close to the escape speed to hang around unfixed, or untrapped in the atmosphere.