RISC-V being based out of Switzerland, the ISA being under a permissive Creative Commons license, and most software tools being FOSS is definitely why it's being adopted here. It's completely isolated from all geopolitics.
The US (certainly the current US) can do that, but (https://en.wikipedia.org/wiki/Arm_Holdings):
“Arm Holdings plc (formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a Japanese-owned British semiconductor and software design company based in Cambridge, England”
If Europe is making a serious investment then it has more than enough power to say "you'll get the contract if you divest of X,Y,Z"
The USA pressures Japan to stop selling licences to European Fabs? Why, what would push them to such extremes?
Fabs can still produce those current designs (they just don't have licences). Now Europe can buy SoftBank out, or Britain can just walk into ARM Cambridge and say it's been sequested for the war effort.
Of course it would only ever come to this if softbank refused to sell and there was some national security angle.
If ARM want to close their office here, then the state can hire all their engineers and offer immunity/void on any NDA they've signed with ARM, if anything that's actually the most desirable outcome.
Again we're talking about things that simply aren't going to happen, and if they do there are much much bigger problems.
Arm even tried to cancel Qualcomm’s licensing agreement back in the fall. Using RISC V entirely circumvents not only royalty payments, but legal battles like that (frivolous or not).
Or perhaps because ARM is miles ahead of risc-v today.