it is not about hiding, it is about not being able to do anything about it. for example in a scenario where there isn't any nodes and there is a mining cartel, they could be bribed by some shitty exchange that got hacked to reverse a bunch of blocks just because that shitty exchange was incompetent and insecure and got hacked. there would be nothing anybody could do since there is no node in that scenario to reject their "less work" chain. this is not even hypothetical, it happened a while ago when Binance got hacked and tried bribing miners but wasn't successful.

the distribution of hash power and the authority of full nodes spread across the globe enforcing the rules prevents that.