To make a 0.500 M solution, one could take 0.500 moles of the solute and add enough water to make 1.00L of solution.
That doesn’t mean add 1.00L of water. If that were the case the concentration would be less than 0.500M since the volume would be greater than 1L. The solute itself occupies some space.
This is why, when preparing a solution of a certain molarity, that we add water until the solution is at the target volume.
1.0 L of water.