The article completely skips over the fact that adults just don't have enough time. Children don't have to raise children, go get their car fixed, mow the lawn.

The article completely skips over the fact that adults just don't have enough time. Children don't have to raise children, go get their car fixed, mow the lawn. They are bombarded with native language at home, at school, while playing with friends. They could not not learn the language even if they wanted to. Whereas for adults, they are not bombarded with the language unless they move countries to be in an immersive environment. In a non-immersive environment you need to dedicate time to learn the language which is a fraction of the time children are exposed to while learning mother tongue.