That's only because it was airburst and the fallout dispersed in air.
Tsar Bomba was very clean relative to the yield.
Even then, it release more radionucleonides than any bomb before it (airburst). They limited the yield to 50 megatons, because fallout in Europe would have been catastrophic from a bigger 100 mt bomb that was allowed by the design.
TBF the 100Mt variant probably wasn't a viable weapon.
As it is, Tsar Bomba was air-dropped from a specially modified Tu-95 Bear, the Tu-95V, which had its engines, bomb bay, suspension and release mechanisms redesigned and fuel tanks and bomb bay doors removed to lighten it:
The bomb was dropped at 10,500 metres altitude and descended by parachute to 4000 metres before detonation, by which time the carrier aircraft had travelled 39 kilometres. Even so, when the shockwave from the bomb caught up with it the plane dropped a kilometre, although the pilots managed to recover. A US aircraft in the vicinity had its paint scorched.
And that was the ~50Mt version.
It's highly unlikely that a carrier aircraft could have survived a 100Mt bomb. Or that it could have reached targets in CONUS when flying from Warsaw Pact territory. Or that a parachute-retarded bomb gently descending towards a target in US airspace during a shooting war could have survived for several minutes without being blown apart by a surface to air missile (which would almost certainly have disrupted its ability to deliver a full, or even partial, explosion).
And as the weapon weighed 27,000kg the USSR would have had problems building an ICBM able to carry a re-entry shielded version (to avoid being shot down).
So: not a practical weapon, but it really gave Nikita Kruschev something to wave in JFK's face.
Just quibbling on a small point. The pilots/plane not surviving the blast would not make it impractical. It would just change it to a suicide mission. A small price to pay in a nuclear war.
And de facto suicide missions were totally a thing in event of a 1950s-70s nuclear war. B-52s didn't have enough fuel to get home after delivering their payloads. Best they could hope for was to reach neutral territory before they had to bail out. Neither did RAF Bomber Command's V-Force. But the V-Force married officers' quarters were alongside the runways, so if they had to scramble, there was probably nothing and nobody to come home to ...
Megaton range bombs have no good use in war. The same weight in 300 - 400 kt warheads covers more area and the destruction is just as good. Rest is wasted in the atmosphere.
50 mt weapon and 100 mt weapon were the same design, same size. The yield was just tuned down with lead. Not enough range for the bomber to be useful.
If you read Sakharov's memoirs, the whole thing was a dog and pony show for international politics. No technical side was consulted before the decision was made and better proposals were turned down. There was no military use or scientific need to make it. When the US and Brits started testing in 1958, Khrushchev wanted Big Bomb to show off.
The Soviets and then the Russians did maintain SS-18s variants with a single 25Mt warhead - presumably for EMP generation or hitting deep bunkers like those at Cheyenne Mountain or Raven Rock Mountain.
Big booms were compensation for inaccurate delivery systems. We don't need them *now*.
They still have a role for an EMP attack or even a thermal pulse attack. A gigaton range bomb in orbit will fry electronics to the horizon and light fires to the horizon.
Wow and I thought the narrative even for Proton as an ICBM was pretty flimsy! A huge loss that Korolev died so early due to his gulag destroyed health as it looks like he could push through what was needed, by any means necessary! :)
Tsar Bomba was very clean relative to the yield.
Even then, it release more radionucleonides than any bomb before it (airburst). They limited the yield to 50 megatons, because fallout in Europe would have been catastrophic from a bigger 100 mt bomb that was allowed by the design.