That's because most students are lazy to study again at home, that's why homeworks was invented. To force them study at home.
The reason why they are "lazy" is because it's "home time". A time where they can just be themselves in the comfort of home and not have to worry about school business.
And while some may say homework helps improove the students education, can't we just accept school has nothing to do with education and it's just a place where children are forced to memorize facts that have little practicality in adult life? That if they fail to remember their "times tables" they're shamed for it.
Heck I was never that good at maths myself... but you know what I am good at? Using a calculator.
Maybe if schools teach us things like mental health, diplomacy and negotiations, domestic care, legal awareness, open-mindedness to various people, standard laws or standard social interactions and responses then I would of cared more about School growing up.
But no, apparently learning the periodic table or the Banana Wars of April 21, 1898 – August 1, 1934 are more valid subjects for our developing brains to memorize for our adult life.
Oh, and apparently there is this "new maths" now that's taught in schools, so regardless if you're bad at maths like me or not, parents will still struggle helping their children with homework on brand new yet just as useless subjects they didn't cover in their time.
The only people who benefit from school are extroverted people, and usually they're only their for social interaction and to see their friends. The day I become a parent, I will try to seek alternative options for my children.