I don't think people understand. The goal was achieved - all the tickets were sold! I know this for a fact because I couldn't get tickets for the first OR the second day. People from all over Punjab and the rest of Pakistan were impatient for this game.
There a few reasons some of the seats were empty and I'll list them:
1) First of all, as my friends who were present in the stadium have told me, most of the people wanted to get the best view possible and therefore didn't bother to sit on their seats, yet roamed around and we're close to the grill to see the action from a closer distance.
2) The match, like any other cricket game was a long one and this photo is of when a lot of people who had come in to watch the game had left. I don't blame them. I went to watch the Zimbabwe series in 2015 and I couldn't stay in the ground for the entire game. It is EXTREMELY hot and humid in Lahore these days and therefore, people are bound to start leaving after getting a glimpse of the action.
3) The goal was to make money and to have all tickets sold - that was achieved by the PCB. The problem is, like another poster has mentioned, a lot of people buy tickets in bulk early on only to later sell them at a higher price in the black market. Most probably their tickets went unsold and the PCB made money anyway.
4) One enclosure was purposely shut down with fans not allowed to enter, reasons must only be known to the PCB.