I’m guessing folks were desperate to ride from X to Y, and the bus company offered a half-price deal on the spot...and some guys just took the deal.
It could be, or maybe whoever loads the luggage into the compartments was looking to make a little extra money, and after cutting in the driver and whomever else needed greasing, went ahead with the plan. I’d guess if they checked records of the people riding like that, they’d find interesting things in any event though.