Why do they have children just to cut them off?
They likely assume their children will be replicas of them I suppose. If they took on responsibilities happily or- at least the rest of their lives were reasonable enough to soften their responsibilities, they probably assume their children's lives will go the same way.
In which case- the child would
naturally progress in to adulthood, without even really questioning why they now needed to take on responsibilities. I don't actually remember anyone when I was 18 that rebelled against that. We all just complied!
Culture plays a big part too. Some people seem to deliberately have children as an additional labour force for the family! Or, it looks that way to me. I know a few families where the older siblings effectively become parents for their younger siblings. I guess they just accept it in many cases because they're too young to question and they may feel genuinely protective towards their younger family members.
That I suppose is a genuine reason. The instinct to protect and provide for your kin. Some people are eager to take that on because maybe they like to feel needed and relied upon.
But no- I doubt many parents have children with the intention of
having to cut them off. They likely assume their child will grow up compliant- like they did. Or- if they are already reliant on the state, they may not have a problem with the idea that their children will be too. They may have enough confidence that they will actually be taken care of.