Why do people who have a long-term relationship and then get married divorce after a maximum of two years?

I see and hear such couples all the time. They get married after ten years of dating and divorce within two years. Do they not know each other during this time? something I saw and heard. Couples who get married after meeting two or three times have a long and happy marriage. Is there nothing left to the marriage after the togetherness before marriage?
Why do people who have a long-term relationship and then get married divorce after a maximum of two years?
Post Opinion