Yes, the game has changed; there are salary caps and more teams compared to the 70’s, but I will isolate some of their downfalls, which apply to any team or organization to this day.
When you have something really working, you don’t make major changes. You find what caused that successful time period. It can apply to one game, the week, the year, it doesn’t matter and you strengthen it.
Case in point, in 1979 Montreal won their 4th cup in a row. Rather than strengthening their successful actions, some major changes occurred, albeit some unavoidable, but nonetheless major changes. In the workaday world we call it “turnover.”