Dish soaps are formulated to remove grease and oil from plastic, glass and ceramic glazed dishware, it works great for this. A quality car wash soap is formulated to clean well without detergents but more than that a quality car wash is formulated to make the washing process slippery to help prevent scratching during the washing process.
What you basically achieve is "overkill". You pull out all the wax and the polishing oils out of the paint over time leading to a dull paint finish. Some soaps have even salt in them so you are applying a corrosion accelerator to your car which as you would know won't be too advisable.
Some are so strong that tey can even harm your clear coat over time. The amazing result might just have been because of along due detailing needed. Do you clay your car by any chance ? Because what simple shampooing leaves behind over a period of time claying helps to remove that. Your detergent just did all of that in one go !!
