why is divorce happen between a newly married couple?/

Yes you're right the divorce is more than past maybe this because of our fast life that didn't give people to think well and to know each other well and the second thing is because love now is not every thing like the past days today money is more important for people than love so that there are no good communication between people every one is busy making money to live, a friend of mine his wife left him because he works a lot and doesn't give her a huge amount of money everyday so she left the home and went to her parrents taking his 2 months old baby with her and asking for divorce while he is very good with her and treating her good and really cares but she wants money not love.

I think they are not understand each other.

there is no rule that each of the married people like another and so these type of cases wanting divorce will be found.