I’ve written elsewhere that you can say “because I said so” with a clear conscience. You are a father. As long as you haven’t squandered or abused your authority, you can write some pretty big checks.
But that doesn’t mean that should be your normal mode of operation. If your children ask “why” they need to do something, you should do your best to answer it, especially if it’s coming from a place of curiosity and not disrespect.
These are often opportunities to go deeper into your values and give larger lessons about the world. I told my kids that they could sleep in the basement in pillow forts as long as they cleaned everything up first. My son asked why they had to clean up the whole basement instead of just the part where the forts would be.
And so I told him they had to do the whole basement because they had made a mess in the whole basement. We also lived in the whole basement, so it’s nice to be able to walk around without stepping on a LEGO brick. It was also ours and so it was important for us to take care of it.
He seemed to accept that answer.
This should all be age-appropriate, of course. As kids get older, they will need more and more of these handles.