Fighter doesn't really need more offense, they can deal the most damage in the game. Taking cleric only reduced offense to gain support.
Past Fighter 11 you don't pick up much offense. Level dips into Cleric are a great way to shore up some of the fighter weak points (no Bless for GWM/SS, Healing Word for helping the party, Guidance for mini-Alert feat), as is a few levels of barbarian.