Being a witness to how pushy-shovey Hindu pilgrims can be, both in the North and South of India, I am however surprised at the extent to which this can occur, leading to massive loss of lives at such a holy place. Some news sources are citing bomb threat as the cause for stampede, while this news source is saying some of the devotees started slipping off the hill causing others to fall on top of each other causing the stampede. Sounds pretty far fetched but from my experiences so far this seems like a more plausible explanation.
They seem to push and press up to the person in front of them because queue cutting seems to be the norm and leaving a gap between you and the person in front invites a queue cutter to exploit the opportunity.
Squeezing yourself into available gaps in order to bypass is also the norm, as is overtaking in queues. Many times a person would tap you on the shoulder and try to push you aside (if you're not aware of what happens) so he can squeeze past you as if you're not in the queue!
They also push and shove because they want to get to point B faster and think that pushing against the person in front will get them there faster.
And of course the insanely dense and out-of-control overpopulation in India does not help.
The really scary times happen when during a massive bottleneck of humanity, another passage or opportunity opens up and then there is a massive push and stampede towards the new opening.
Put it all together and its a stampede waiting for even the most inane excuse to happen.
When even a simple thing as queueing for a temple darshan becomes life threatening, there is something wrong with the whole setup here.
On the TV a reporter lists down a long history of similar stampedes that have occured in other temples in India.