What is allowable in the Xcel Code of Points may not be allowed by a team coach for a variety of reasons. The most common reason is that competing unnecessary skills incurs unnecessary deductions. If my memory is correct, an illusion doesn’t satisfy the full turn requirement on floor. If a gymnast can’t perform the skill with near-perfect execution, they will earn a lower score than if they just removed the skill entirely from their routine. Strategizing about routine composition is a skill that takes many years to develop, which is why many coaches impose more constraints on “allowable” skills at lower levels.
For example, my gym has a “zero-deduction” policy for floor routine dance choreography. A gymnast is only allowed to compete dance skills that serve a specific requirement. All other dance choreography must not incur any deductions, which means gymnasts aren’t allowed to compete extra dance skills that are recognized by the Code of Points.