It is simple: you never did it before!
Do you ever remember in your life spending 5 minutes doing circles or diagonals with your eyes?
These are simply not practices you are usually used to.
You don’t train these in schools or at the gym and your perents never mentioned it to you.
Brushing your teeth is natural because you have conditioned yourself to do it.
If you don’t brush your teeth, you feel like you miss it.
After around 3 months or eye training practice, it becomes, natural and grounded in you.
It becomes as easy as washing your face or doind a few stretches.
But because of lack of experience, and practice in that field, it will take at least some focus and discipline to ge used to these exercises in the beginning.
Count 3 months to integrate and fully master the techniques.