ELI5: why child support is based on income rather than what a child would need monthly.

This is exactly the life of my sister right now. She was married and had four kids with her husband. Her husband was pretty much a dead beat dad for the most part while only caring about trying to get weekend gigs as a DJ and talking about hoping to get into acting someday. He brought in almost no money ever, while my sister worked a full-time job and then also took night classes after work and came home every night to him in the back room on his game system, asking "what's for supper?" as soon as she walks through the door, oblivious to the fact that the kids were not clean, fed, or even accounted for, and the house was trashed. Fast forward a couple of years and they get a divorce and dad gets hooked on painkillers and mom ends up with a guy that ends up molesting her daughter and is sent to prison. Her lawyer was a total cunt and completely roasted her at court for some fucked up reason that fit her agenda. Dad gets full custody and mom only gets supervised visits every two weeks on the weekends, and the child support he gets is way more than he's ever made in his life. He ends up in the city mission with all four kids for over a year because of his addiction and not willing to work. His oldest son, my 14 y/o nephew at the time, got a job and started making money and I think it woke his dad up, because he got his dad a job under him at the company that he worked at after school and on the weekends. Dad ended up getting fired and my nephew quit out of embarrassment and neither has had a job since then. My sister has held a job for awhile now and has an apartment that they all live in and she's the only one working. Crazy thing is that my sister is now dating and living with the guy that she cheated on her husband with, and her ex husband, and the four kids and she's the only one that works. Her drivers license is suspended because she's behind on child support and drives illegally to work each day to pay the bills, and her paycheck is still the only one in the house, even though the person that she pays child support to and all four of her kids and current bf all live with her and don't help at all because they don't work.

/r/explainlikeimfive Thread Parent