1. ARM doesn't own any factories. Its entire workforce publishes blueprints for making chips (like a software company where the entire asset is intellectual)
2. Buying this type of intellectual asset, means owning and controlling a technology.
3. This also means, all the other customers who depend on this tech (Apple, Samsung, Amazon, pretty much all big tech companies) are now at a disadvantage with NVIDIA as a competitor.
4. China heavily depends on ARM (Huawei, the company's biggest tech manufacturer rely on ARM)
5. This means, the after ARM gets owned by a US company, the US can possibly just cut-off ARM supply to China
6. Since ARM is basically like a software company, it's better to not be owned by a hardware maker. That way, it can prioritize demand from several hardware makers instead of being directed to cater to one market)
So, all-in-all this is a good thing :)