It was not the final the crowd wanted and the stands showed that

Although more people filed in in the minutes prior to the clash, the stadium was not as full as the organisers would have liked.
The local crowd wanted a Real Madrid v Barcelona final. It is no secret that they are the two clubs with the biggest international following and is one of the most watched clashes in the world.
For the Saudi fans, a Madrid derby was better than nothing, but many would have preferred Barca to reach the final instead of Atletico.
Therefore, the attendance was down on what was expected because even though the gates opened four hours before the game, the stadium only had a respectable look to it partway through the first half.