Even SRK in Dear Zindagi was dealing with a supposedly troubled divorce.
It is less about the concept being outdated, and more about how everything is changing now.
The focus is on making movies which millennials can relate to, their struggles, their views on marriage/romance/relationships and the debate surrounding it. These problems did exist earlier too- divorce, adultery- but no one really talked about them.
As we are moving into a more modern...erm freer time I guess, the representations of love are also changing onscreen. It doesn't have anything to do with younger actors or older actors.
Kapoor and Sons was such a game changer, reflecting on- being gay, a long-term marriage in trouble, as well as new age romance.
The point is millennials have more of a choice and say regarding how they lead their life vs let's say baby boomers or Gen Y. And that is what is represented onscreen.
So, yes, it is not an outdated concept in younger Bollywood as you ask, it just a way to cash in on the innermost conflicts people face today but most of the time they are grossly misrepresented.
Movies have also started bringing in the nostalgic element by remixing old hindi songs.
Off topic: The focus is on too many other things now like ambition, challenging ideas, changing perceptions so the old ideas of hunky dory romance takes a backseat.
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