Issues of sharing data between Angular components | why do we need state management like ngrx?

In this video, I show you the issues we face when state management like NGRX is not used .
In this video passing data all the way from childA component to its parent component and then to childB component is very complicated.
Here is the link to the code on stackblitz,

why to use ngrx?,why do we need state management like ngrx?,