Yet Satoshi wisely saw this as a non-issue. If anyone actually commits the massive amount of time and money to build up that much mining power, they benefit much more from keeping the system running smoothly. By cheating the system, they make a tiny gain but undermine confidence in the system as a whole, which tanks the market and makes all their time and money spent worthless.
Reflections on the Best Blockchain Tweets Ever Written
Daniel Jeffries

Would large incumbent blockchains have incentive to 51% attack young and small competing blockchains?