But any time someone points that out to them, some other helpful Euro jumps in to say, "well, large metal structures and lightning don't mix. And thunderstorms in the US are no joke!"
Which is of course true, but that's also precisely why large structures like that are thoroughly grounded, isolated, and shielded where necessary. We don't stop playing indoors when there's lightning.
And then another helpful Euro stops in to say, "Well, it would be dangerous as the fans enter the stadium."
Which is really funny, as if FIFA or anyone else cares about the fans entering the stadium. TV time slot, viewership, and ratings, are what drive the decisions.