Not just that, many don't actually care about an oath.

They aren't raised to view that as a taboo.

They've never had to rely on someone's word for anything important, have them fulfill it, and realize what it means... and what it means to give it and not keep it. Everyone just lies, so they lie, and everyone expects that everyone is lying, in their minds.

So an oath? That's just something you say to get the job, and only something you keep because there might be a punishment if you break it. For many, principle is a foreign concept.