Because as per available news reports (also posted here) that it was like cloud burst due to 11 inches rain.
The river have so many tributary nullah and due to heavy raining river overflowed.
It is called Flash Flood
The small bridge is standing undamaged
At...
more... midnight no one can be blamed specially when it's raining heavily and just 8min before nothing abnormal observed on the track.
Rail embankment washed away and it happens due to water current Remember hanging tracks picture of Rajasthan_Gujarat ?