Acquiring this much of the total supply can be extremely expensive — and in some PoS-based blockchains, it be nearly (or completely) impossible. When crypto tokens are staked into nodes, they are locked for a pre-determined amount of time. This means they're removed from the marketplace and can't be bought. If more than 50% of the total cryptocurrency supply for a given blockchain network is staked, a 51% attack becomes extremely unlikely, because for an external attacker (i.e. someone not already invested in the network), buying up or otherwise being able to control enough tokens to control more than half the nodes on the network becomes almost impossible. And there's a second layer of security here, too: if someone does buy up such a huge amount of tokens that they could gain control of the network, they would then be disincentivised from wanting to attack the network simply because attacking the network would harm the value of their tokens — once they're invested, they're simply better off acting in good faith, so their tokens gain value rather than losing value.