In What Scenario Might a Miner Accept a Lower-Fee Transaction over a Higher-Fee One?

A miner might accept a lower-fee or zero-fee transaction in several non-standard scenarios. They might include their own transactions to ensure immediate confirmation.

They could be fulfilling a pre-arranged, off-chain agreement with a specific user or organization. They may also choose to include older, lower-fee transactions to clear out their local mempool.

Finally, they might be running a non-profit or altruistic mining operation with different priorities than pure profit.