Why do young child struggle in daily routines?

Because their brains aren't as developed

I wouldn't say young children struggle with daily routines. they are learning and developing so routines need to be kept to the minimum so that they can do them

The part of the brain that controls executive functioning isn't fully developed until a person is 24. A 3 year old had a long way to go.

Because they are used to just playing all day with NO responsibilities.

Mostly poor parenting with parents that act like gorillas instead of humans..and actually a lot of human parents are less nurturing than gorillas