It's a nuclear weapons thing. Basically you want your entire nuclear weapons supply chain infrastructure to be in your own country. These days that also includes super computers to do simulations on what happens with your aging asrenal (just look at how many Top 500 supercomputers are at national labs like Oak Ridge, LLNL, or Sandia). Japan doesn't technically have nuclear weapons, but they're rumored to be "a screwdriver's turn away", or practically within a few weeks of having a weapon. That posture itself requires even more simulation just to be sure you can make good on that.
The AI stuff is basically "well sure, these are really good at distributed matrix math, why not?" hoping to get better volumes and make the program cheaper internally.
And they're working on getting chips fabbed in Japan too now that IBM sold their 2nm process to Rapidus, but that's probably successor to these. Maybe 2028? In the meantime there's still more nuclear simulations to run than there is compute to run them.
The AI stuff is basically "well sure, these are really good at distributed matrix math, why not?" hoping to get better volumes and make the program cheaper internally.
And they're working on getting chips fabbed in Japan too now that IBM sold their 2nm process to Rapidus, but that's probably successor to these. Maybe 2028? In the meantime there's still more nuclear simulations to run than there is compute to run them.