100Mt Nuclear Bomb why not?

I've read some articles in the websites about the effects of radiation from a Bomb. The Nuclear Bomb Tsar 100Mt was designed and scaled down to 50Mt, due to the deadly effects of nuclear fall outs. Regardless of what the effects of the bomb, why didn't the government of whatsoever decide to detonate the Bomb somewhere in the Sahara desert? Since a 100Mt can be very devastating, Sahara is the worlds biggest desert ofcourse. I saw the 50Mt Bomb, i liked the 100Mt more.