Marriage is not girlfriend/boyfriend.
It's far more serious, and making it a commitment to be contemplated deeply before entering - and not easily breakable - is the whole point of highlighting the problem of trivialising it.
Marriage is rooted in religion, for better or worse, and these thoughts about making marriage some unbreakable for-life bond are based on religious beliefs hundreds of years old. Catholics couldn't divorce, ever! We live in a more enlightened age, one where religious thoughts have less to do with forging our societal beliefs. Can't we progress with our thoughts on marriage as well? Marriage for life would mean for many an unhappy and unfulfilling life. Perhaps a life of violence or depression. Is that we want to force people into? A life without choice, a life without happiness?
So it’s not wrong to say marriage has its roots in religion, but the cause to create marriage hasn’t gone away even if religion isn’t a factor: Can you imagine how difficult it was for a single parent (especially women) to raise a child alone, a few millenia ago? I think it’s fair to say that it caused major problems.
Even today raising children is still extremely difficult. Raising a productive citizen is another order of magnitude of difficulty.
Around a billion people, give or take, in China would disagree with you.
Heck Japan isn't exactly a religious country.
With a few exceptions, the concept of marriage coincides with agricultural societies.
Also, parents invest a lot in their child's marriage, e.g. downpayment for a house, car, etc, for their child (singular!), so that adds even more pressure to "make things work".
Ecclesiastical annulments are grossly misunderstood by most Catholics and non-Catholics alike[1]. They are not "Catholic divorce." And yes, the tribunal system can be gamed, but if you actually believe you should realize that God isn't going to be fooled. And if you don't believe then why do you even care what the Church thinks?
[1] See below reply
Because your friends/neighbours/relatives may be Catholics, and you may care about your appearances.
In my experience with religious folks, keeping God happy is not the sole driving force behind most of their lives to the exclusion of all else. It's a framework around their lives, but not always priority #1.
Given that, annulments are essentially a catholic divorce, with a little bit of magic added.
Think about how many people within your own extended family do this? Take a guess, deliver this talk to them and track through life how many follow the path.
We chimps display a wide spectrum of Personality traits and an even wider spectrum of Needs, which are constantly changing through life and the events that effect it. Dangerous to assume whatever system you have accepted will be accepted by all.
Its easy to come up with all kinds of theories about "what works" and "how things should be" but that is usually based on our limited awareness of the spectrum.
How come you suddenly need 50% less emergency cash per person just because you're married?