Because if we've rolled Red Sonya, Gray Mouser and Elric and are planning to raid the temple of the crocodile god the last thing we want is for our 4th to be Dudley Do-Right.
We want to loot the religious artifacts, seduce the holy virgins and maybe engage in some light arson to cover our escape.
We need another quick wit and strong arm not some whiny wet blanket going on about how desecrating bodies, stampeding sacred crocodiles and un-holying the holy water is somehow 'wrong'.

Alignment in general adds nothing useful to the game but lawful good is especially galling. It seems designed to get in the way of the right, honest sword and sorcery upon which this hobby was built.