Some fraction of the motivation had to be "Dude, how cool would that be?"

Quite possible. "Our ICBM's can't hit shit, so we'll just fry half your state".

or...

In Soviet Russia, bomb drops YOU!

Perhaps, but I'm sure part of the reason was because "better accuracy" just doesn't make look as good in a propaganda film as "GIGANTIC FUCKING EXPLOSION HOLY SHIT."

Bombs this big are useless militarily.

Unless you, like, drop one on an enemy city.

This particular bomb was dropped from a specially modified bomber, and had the yield *reduced* so that the bomber crew would have a chance of escaping. It was way too huge for an ICBM.

The original design was about twice as powerful (~100 MT instead of 50.) Several of the stages were replaced with lead to limit the power of the bomb.

It was one mean motherfucker.

At the insistence of Andrei Sakharov, who was starting to have second thoughts about the whole thing, the bomb was built with a pusher/tamper made from (I believe) tungsten carbide instead of U-238. U-238 won't sustain a chain reaction but will fission given a high enough neutron flux; that was what reduced the yield to 50 MT.

Congratulations, shinji, congratulations.