[DC] Why is it even necessary to appeal unenforceable executive orders in court instead of just ignoring them?

I guess I don't understand how legal system works, but I wonder why do we even need to appeal executive orders that contradict laws or condition, and the ones where President does not have a legal right to sign them?

If they are clearly not legal and unenforceable what are we suing for? Is the court supposed to say that illegal thing is illegal?

I guess this is a stupid example and exaggeration is not a way to proof anything, but if I come to the supermarket and give them the order to stop selling carrots they are just going to laugh at me.

I guess this is different from President signing the orders that he cannot sign, but how is it different?

If he tries to control funding approved by Congress although he clearly cannot do it why do we need to appeal this decision? Isn't is supposed to be void just because this is outside of his jurisdiction?

The same thing with 13th amendment. Aren't we just supposed to follow the Constitution and ignore the orders that contradict it? What should the court do? Even if the court blocks this decision what would it change if the decision was not legitimate from the very beginning?

I'm just curious about how legal system works and why we are supposed to put so much time and effort into fighting against the stuff that cannot be enforced anyway.