Why is That? 

As we know different type of traders trade in three different time. 

1. Morning Trader (Momentum)

2. Evening Trader (Sideways)

3. Closing Trader (Breakout)

Morning Traders : are mostly those trader who are Option Writer and Squaring Off Overnight Position hence a good momentum can be seen in the morning. 

Evening Traders : after approx. 2 or 3 hrs momentum get exhausted and marketed will goes into sideways, this is the time when trapping mostly happened or trend continuation.

Closing Trader : before 1 or 2 hrs of Market Closing morning will square of their position or breakout can happened hence a good moment can be captured.