Imagine there's a place you want to get to along with a lot of other people.
It starts as a nice queue and is pretty orderly but then some people start pushing in and trying to jump ahead in the line. Other people see this and try the same thing. If there's no good exit or crowd control then the back of the crowd slowly pushes against the front until disaster occurs.
People in the back have no idea that there is nowhere to go but they've been standing for hours and want to keep moving forward.
Yeah except for me, the sheer existence of the crowd makes my brain go "avoid avoid avoid at all costs".
I even go shopping in the middle of the night or very early morning when stores first open. I don't mind a few people but a crowd will make me turn around immediately. It is some kind of primal fear to me that shouts danger.
Apparently a great many people don't seem to have that survival instinct.
It's not necessarily a survival instinct, crowds aren't inherently bad, and they rarely result in death or injury -- what if the crowd you're avoiding is the big line for fresh water after a disaster, waiting around until the crowd dissipates may mean that supplies run out.
That mecca thing recently blew my mind, they just all crushed themselves to death and kept going.
The mecca death toll is now near 1500 people I believe. 1500!