I was always skeptical about why it can't be stopped; why they cannot stop it
Bitcoin biggest strength remains it's resilience from being decentralized and the fact that world government are not fully centralized.
China outrightly banned Bitcoin, others didn't.
Another maybe minor reason it was left was that it wasn't considered a threat.
But, how much money do you really need to run a 51% attack, and then render it worthless?
51% wouldn't directly render it worthless perse.
It's biggest strength is allowing double spending and maintaining it isn't really viable with cost.
They can't attack it, because that would reveal who they are.
Hope you are aware that 51% attack isn't the only attack that Bitcoin can face.
Stricter regulations is one (we facing it now) and it's more subtle.
such as the EU's MiCA and U.S. proposals for stricter KYC/AML compliance.
Like I said above, Bitcoin biggest strength remains decentralisation
Rather than attacking, the government realize it's better to coexist
More like with Gold.