I would presume the quoted price for the charter included the en route fuel stop. Avoiding that fuel stop (thinking they had "enough" to make it) would have increased the profit margin. Commercial decision gone bad? Pure but reasonable speculation. It's been done before.
Came up with the same thought, especially as I heard it was the airline owner who was one of the pilots. Can you imagine challenging his decision not to stop en route as planned. Instant South American equivalent to the P45.