The divorce rate is not correctly tabulated.
You have serial divorcers.
You also do not have an accounting for re-marriage to the same person.
When you factor the latter in the divorce rate drops to the 30+% range.
That is still very high, especially if most of those are due to "irreconcilable differences."
Regardless, when the divorce laws were eased you redefined marriage from a permanent union of a man and a woman to a union of convenience, expected to last only until someone better came along. The Biblical command that what God had joined let no man put asunder was tossed right into the dumpster. The traditional concept of marriage got pitched at the same time.
Thanks for mentioning the serial divorce cases. I had never considered that factor into the claim that 50% end in divorce. It makes the picture look a little better to recognize that.
What was it 60 years ago? Exactly.