How Does a Hard Fork Often Become a Solution after a Major 51% Attack?

A hard fork is a permanent, non-backward-compatible change to the blockchain protocol. After a major 51% attack that results in significant financial loss (e.g. a deep reorg), the community may agree to hard fork the chain to a state before the attack occurred.

This effectively rolls back the fraudulent transactions and creates a new, corrected chain, abandoning the compromised history. It is a last resort due to its contentious nature.