Maybe they feel as if they have to be strong in order to still be able to support their child. Maybe they hope that their positive influence will rub off on them. Or, maybe they just tell themselves it's nothing they did wrong (whether it was or wasn't.) That they're doing all they possibly can to support the child and so- they needn't feel guilt.
I know what you mean though. That's the personal reason I'm antinatalist. I couldn't bare to see my child unhappy. It would break my heart. And, I feel certain they would be. With a proportion of my genes, they'd be screwed from the start! I love them too much to expose them to this world and my (no doubt) useless parenting in trying to navigate it.
Maybe some are like that. But also many are just simply assholes, they just don't realize it
Life itself is already hard WITHOUT kids. So to even include KIDS (sometimes even multiple), it's just simply a recipe for disaster
It is a mess right off the start. So to add too much positivity and reasons to it later on, is mainly just a fantasy
These days and age, with living cost rising, you begin to see retired "parents" with their paid off houses, while the "kids" are moving into their cars / vans / RV, or with roommates
Yet the parents are "okay" with this
That says it all