In the 1960's the average age of a couple getting married was 22 and 20. They likely had no more than one bank account each. Credit cards weren't extremely popular. Student loan debt was minimal by today's standards. The couple typically started their financial life together, and whatever they built was owned by the couple together - the average couple didn't have much in the way of premarital assets, and likely not much premarital debt either. The divorce rate would more than double between 1960 and 1980, but was relatively low. Together, the couple may have a handful of monthly bills.
Today, the average couple gets married at age 30 and 28. Each spouse is likely to have multiple bank accounts and several credit cards. One spouse or the other likely has student loan debt, and it's not unusual for the number to be above $50,000 or even $100,000. Their parents are also older, so it's more likely that one or both spouses have received or are expecting an inheritance. They're both likely to have started retirement accounts. One or both spouses are likely to have owned a house - often one spouse is moving into the other one's residence. And the divorce rate, while lower than the peaks of 20 years ago, are still far higher than in our parents' generation. Between monthly subscriptions, payment plans, multiple cars and potentially multiple pieces of property, the couple is likely to have two dozen monthly bills or more. And most importantly, couples come into the marriage with a decade of financial habits, which can be harder to change than any of the previous facts.