I think everything you listed is partially to blame....when the general vibe of the festival hours before opening is "Lets stampede this security, break down these walls, trample people etc" something has already gone horribly wrong.
I don't want people to blame the music, I was at run the jewels at a well managed music fest (safe lines, no check point issues), no issues beyond fear of second hand smoke.. it's either a toxic parasocial relationship.. it a full on lack of care
i know im going to get a lot of hate for this (and maybe even moderation action)... but saying that travis is all the blame would be wrong... even with that video though it is absolutely horrible... in a crowd of over 50000 people (probably more because of the many who barged in and put it overcapacity), and on a huge stage, and up high he might not see how bad it was.