I read somewhere, and this was early Saturday so maybe it was an unsubstantiated report, but that most of the people were gathered near the main stage expecting Travis Scott to appear there. When he started his act, he was not at the main stage which cause a rush of people to wherever he happened to appear.
Apparently crowd crush does actually happen fairly often, but obviously not to this extent. Large crowds move as a fluid when they are packed in too tight. I’ve read reports about many concerts where this happens and while people don’t lose their lives, it’s a scary and traumatic experience.
Live Nation doesn’t seem to have a great safety track record, and I believe that this is where the lawsuits should be directed for the most part.