Please note that it's not the first time it collapsed,
It's collapsed four times before under heavy snow.
It's an air-supported structure, so as soon as the first tears occurred, the air-pressure that holds up the roof escapes, and the roof sags. As it sags, instead of being an arch distributing the weight, it becomes a bowl, concentrating the weight, and the roof material tears dumping the snow. They'll probably have to drain the rest of the snow/meltwater out of the dome before they can even begin to work on fixing it.
It's an air-supported structure, so as soon as the first tears occurred, the air-pressure that holds up the roof escapes, and the roof sags. As it sags, instead of being an arch distributing the weight, it becomes a bowl, concentrating the weight, and the roof material tears dumping the snow. That makes sense. What does not make sense is building it is a place where you know damn well you are going to get heavy snow loads. I'd assume they have some procedure or requirement for reducing that load before they would allow 60,000 people in there for a football game.