The problem is, the only way in and out was ONE tunnel. The place itself was suited for max 400.000 people but awaited were more than one million. The place was exept of this on small way a completely closed factory/trainstation complex. No ways for people to flee, no way for security to get in and help the people.
To blame is the organizer and the authorities for only thinking, how they get money out of this without listening to the many warnings about the place, the entryways and other problems.
They were told before that exatly that could and would happen.