The big difference between the practice swing and the actual shot is the ball. I know that sounds obvious, but when you make your practice swing you don’t care about where the club face is pointing nor the path it’s on. When you put a ball down, you do care where the club face is. Subconsciously you know if you make your practice swing you’ll either miss the ball completely or hit it so far wide of where you want to you’ll be shocked.
If you’re feeling brave and have a trusting friend, set up video from down the line. Set up to it, close your eyes and have your friend either leave the ball there (20% of the time) or move it away (80% of the time) and once he says go just swing (eyes still closed). Do that a few times and watch the video. Either you’ll learn that you should just make your practice swing or you’ll understand why you don’t.
Bottom line is if you want your actual swing to look like your practice swing you have to learn how to swing well enough for that to happen.