Because of that very reason, the work was stopped and at times, slowly started and stopped again. That was one of the reasons why the tunnel collapsed as the work had been on and off, which, if you know any details about this type of work, you'd know when moving mountains and creating tunnels, the soil has a limit. In Pakistan's case, these areas have mountains made out of soil that's like sand, so unless you put a concrete structure around it very quickly, if it sits there, it'll collapse. Go ask someone who lives in the northern part of your country. They'll tell you the same thing.