Because a happy and healthy home life should be centered around a couple's love for each other, not the fact that they share a kid together.
Were they going to get married if she
hadn't gotten pregnant?
It's bad enough when a happily married couple gets pregnant unexpectedly. At least they have a strong foundation with which to work through any difficulties. At the end of the day, they share a strong love for each other, and that will help them work through raising a kid they hadn't planned on having.
But if the couple is "meh" about their relationship to begin with, and then you throw an unwanted pregnancy in on top of that, that's a recipe for a hugely dysfunctional family, and a poorly-adjusted child. Maybe you're right, maybe they're the exception to the rule and they'll pull together, realize they were deeply in love all along and that they really wanted kids all along, and they'll be a happy family that stays together for life. I'm just saying statistically, that's not very likely.
They obviously care enough about it already to take their relationship to the next level and not have a broken home before its even born.
Right. They're considering the next step (marriage)
because she's pregnant. Not because they can't imagine their lives without each other.
Just because people get pregnant by mistake, or whatever proper terminology you want to use, doesn't mean they wont love the kid and provide for it any less than if they had planned it.
I think statistics would disagree with you. There are an awful lot of single moms out there who didn't intend to get pregnant, and are now having a hard time providing for it without daddy around.
I've heard it said that a child magnifies a couple's relationship. That is, if you are already deeply in love and committed to each other, then a child will just make that family even stronger and happier. But if there are cracks in your relationship, then introducing a kid will magnify all those little annoyances that you've been biting your tongue over. Sleep deprivation will make you irritable and edgy and prone to lashing out. The case you described sounds like it's shaping up to be the latter, but I'm just going off of what you've written here, I know nothing else about the couple, I'm just playing the odds.
Not sure why you would think that is automatically the case.
Statistics, mainly. Couples that stay together for the kids are less happy than couples who were already happy and deliberately had kids.