Probably because we're all connected by love. And we're emotional.

We will cry about being lonely & unloved otherwise, so it doesn't matter.

Well humans and their hormones. Plus movies and tv shows hype what is to be in love

Just remember that so called romantic love is nothing more than pheromones and hormones. There probably is more to filial love once someone grows on you or that someone is family (i certainty love my kids).

Because they had "faith" it would all work out in their favor because they thought they were "special" due to their imagined undeserved "privilege" for being born and believed in their hearts that bad stuff only happens to "other" people.
Or I may be full of shit on this one.

Because love is hard work. The minute you stop working for it, feeding it, and caring for it, it'll start to fade.

Because they are chumps.

Sometimes it just doesn't end up working over the long haul. Relationships last for as long as they last. Not every single one needs to be a forever affair.

People wind up in tears because they stay around long after the relationship has run out of gas instead of moving on with their lives.

It's because they suddenly wake up and think to themselves 'what and who did I get myself involved with' and we have kids, how did that happen, what was I thinking.

I might feel a little queasy, but l never cry when falling in love.