why would Saudia NOT fly it with its own metal?
Because at the time of the agreement, they didn't have the appropriate equipment to fly the route, the 777 was too big, MD90 didn't have the range. There is traffic consisting of Nepalese farmers heading to Saudi, but they were generally bussed to India to get flights, the idea of the direct service was to serve them, having GF code share also made sense as vacation traffic from Europe could also be picked up.
Mutt