Upon this question, in various forms, hinges the plots of countless novels, TV soaps and movies.
First two thirds is about the individual struggling under the oppressive weight of expectations and rules imposed by their background, society, church, boss, parents, spouse or even children - then comes the decisive moment in which the protagonist asks themselves or gets asked "but what do you want?"...
And then the dawning realization of failure to live-up to the highest modern morality: self-fulfilment, self-expression (self-ishness)... after which the protagonist breaks free of their background, parents or family - and is met by the intoxicating joy of... whatever.
As Saul Bellow used to argue (and he would know; being a prime example of it), the masses are 'The Romantics' now - and attitude which used to be expressed by a handful of Dichter und Denker (poets and thinkers) is now mainstream: the individual sees himself (more often herself) as standing against everybody and everything else; and as in the Economy chapter of Thoreau's Walden, the prime question of life becomes how to get the most from the world in return for the least amount of effort.
At an instinctive level, most people recognize that this perspective is evil, but in a secular society there is no compelling reason not to reject demands and duties when they become aversive and if you can get away with it.
(After all, you only live once, you have a duty to make the most of your time, everyone is doing it, in fact it is our duty to fight oppression - so divorce is an act of heroic rebellion...)
Why not? If it something make me feel happier - if it is what I want; then why not do it?
The only true answer, the only compelling answer, requires a religious understanding of human life, and of the life of humans.
Lacking that, we will get what we are getting.