There are numerous reasons starting with the shidduch process itself. We expect two people who barely know each other make a decision in 3-4 weeks after meeting less than 10 times; get engaged and barely talk/see each other during the engagement period and then get married and expect everything to work. In the 1960’s and 1970’s people dated (courted?) for a number of months before they even thought of getting engaged.
In addition, we live in a society where we don’t allow our children to experience adversity and build a coping mechanism to deal with it. They come into marriage and don’t know how to deal with the slightest test and immediately give up.