both stablecoins (and many others) are implemented as tokens on other chains, mainly Ethereum but also TRON, BNB and others. So you would need to 51% attack these chains to attack assets on these chains. Leaving aside, 51% attacks will not work for Proof of Stake based chains like Ethereum, it is more like 66% if not more.
A more feasible 'attack' would probably be to just make the private companies black list addresses like they did last week with the bybit hack.
A more feasible 'attack' would probably be to just make the private companies black list addresses like they did last week with the bybit hack.