The worth of a loyalty is set on the day someone hands you a free exit and you refuse it.
An oath sworn by the life of Yahweh changes the price of changing your mind, and that price governs behavior at the hour loyalty starts to hurt. An exit offered free and refused out loud stops being an exit at all; a person bound in advance to either outcome stops renegotiating each morning, and the strength most people burn on staying undecided goes into the work instead.
Choosing a king on the day that king walks out of the city with nothing prices the choice at the bottom, where no advantage on offer could be mistaken for the reason. That set the emotion, the emotion set the marching, and within days a foreigner was carrying a third of the army. Answering with a maybe would have kept those men out of danger and lost them everything the oath bought.