I think there's been a major change in attachment styles, over the time in question, and the needs of most individuals in relationships have changed too, this is to do with changes in patterns in working life, in family culture, in popular culture and I'd say that a lot of the public or social "scaffolding" around individuals, basic stuff like unanimity of purpose, social attitudes etc., is gone too.
That means that people are more inclined to cheat or experience "mid-life" or "quarter life" crisis and cheat on partners or believe they have missed chances by getting into committed relationships earlier in life. Its just my take on things.
There's research suggesting that consequential thinking which used to develop in individuals by the age of sixteen or seventeen is now only developing by the age of 21yrs or 23yrs of age. Strictly speaking consequentialism is one of those things which is discussed more as an ideological precept or social construct than objective fact these days, whatever, the point is that comprehending it and practicing it is individually and socially advantageous, most of the time, and its less commonplace.
Attachment isnt the whole of it, its part of it, a significant part though.