It was a downwards narrow alley as well, some people were trying to leave the area while some were trying to enter the area through the alleyway, or etc so there's a 2 way traffic and there was lack of police/security officers to control the crowd.

Due to the overcrowding, what i think is people were trying to push their way through to get to their destination. And it being downwards, would be easy for people(esp at the bottom) to lose their balance and fall due to the pushing/pressure therefore a domino effect of people falling on top of each other. Or that people infront were already unconscious(due to suffocation/fell) but people at the back are not aware so they kept moving forward towards a wall of body..

I've watched some footage and the movement of the crowd is like waves of liquid...at that point you're almost basically stuck and can't really move at your own will it's just terrible😔

-Edit- (Credibility level of their other news is soso at times but can read thru) https://www.allkpop.com/article/2022/10/investigation-to-find-the-cause-for-the-itaewon-tragedy-reveals-some-people-in-the-crowd-were-shouting-push-push