Speed post to bengaluru routed through Mumbai

Though there are many direct flights from Goa to Bengaluru, and Bengaluru is closer to Goa than Mumbai, it appears that speed post letters from Goa to bengaluru are routed through Mumbai leading to a delay of one day or more in delivery.
It would be interesting to find out the reason why the mail from goa is routed through mumbai, when it has to be delivered in south india , why it is going to the north and then again to the south . A more efficient way would be to send it directly to the south from goa