What Is the Economic Incentive for an Attacker to Execute a 51% Attack on a Small Coin?

The primary economic incentive is double-spending. The attacker deposits the coin on an exchange, receives another asset (like Bitcoin or fiat), and then uses the 51% control to reverse the original deposit transaction on the blockchain.

This allows them to keep both the deposited coin and the withdrawn asset, netting a profit. Small coins are targeted because the profit from the double-spend often exceeds the low cost of renting the necessary hashrate.