I have been teaching handling to obedience students for a long time. Some students have no issue incorporating and even changing their handling to use specific footwork. But most students have a lot of trouble keeping their footwork consistent.
It might be easier without the dog and without a judge calling the heeling pattern. But insert the dog or the judge into the picture and you can get a stressed and paralyzed handler that get tied up into foot placement thoughts when there is a lot more handling to think about. These handlers worked many days, weeks, months, and some had worked years perfecting the footwork without the dog.
Why does this happen?