That's not what everyone thinks.
NVIDIA already has an CPU architect team building their own ARM CPUs with an unlimited ARM license.
ARM doesn't give NVIDIA a world-class CPU team like apple's, amazon's or fujitsu. ARM own cores are "meh" at best. Buying such a team, would also have been much cheaper than 40b$.
Mobile ARM chips are meh, but nvidia doesn't have GPUs for that segment, and their current architectures probably don't work well there. The only ARM chips that are ok-ish are embedded/IoT at The UK appears to require huge R&D investments in ARM to allow the sale. And ARMs bottom line is 300million $/year in revenue, which is peanuts for nvidia.
So if anything, ARM has a lot to win here with nvidia pumping in money like crazy to try to improve ARM's CPU offering. Yet this all seem super-risky because at the segments ARM is competing at, RISC-V competes as well, and without royalties. It is hard to compete against something that's free, even if it is slightly less good. And chances are that over the next 10 years RISC-V will have much better cores (NVIDIA themselves started replacing ARM cores with RISC-V cores in their GPUs years ago already...).
Either way, the claim that it is obvious to everybody what the 3D-chess being played here is false. To me this looks like a bad buy for nvidia. They could have paid 1 billion for a world class CPU team and just continue to license ARM and/or switch to RISC-V chips. Instead they are spending 40 billion in a company that makes 300 million a year, makes meh-cpus, is heavily regulated in the UK and the world, has problems with China due to being in the West, have to invest in the UK which is leaving the EU in a couple of weeks, etc.