why do some people get married and then divorce and then remarry the same person. why go through the pain of divorce just to get back ?

Question

I also feel like breakups and divorce happen for a reason and people should stop trying to fix what's already broken

Answer 1

They obviously think they can make it work. 

Answer 2

From an early age people practice serial monogamy. Break ups are a dime a dozen.  They start their marriage with this same broken mind set.  "something goes wrong so I should divorce".  Which means the divorce is undertaken as lightly as the marriage was. It wasn't broken.