What are you basing this on?
> it's not like more deadly nuclear weapons would change anything
We haven't been chasing yield in nuclear weapons since the 60s.
Our oldest warheads date from the 60s [1]. For obvious reasons, the experimental track record on half-century old pits is scarce. We don't know if novel physics or chemistry is going on in there, and we don't want to be the second ones to find out.
I can safely say that nuclear simulations are one of the major drivers for HPC research globally.
It is not the only one (genomics, simulations, fundamental research are also major drivers) but it is a fairly prominent one.
Think about a baseball-size device able to take out a city block.
Then think about an escadron of drones able to transport those baseballs to very precise city blocks...