Is polishing a car easy?
Machine polishing a car is a skill like any other and needs to be learned and practised. Experience also helps.
It is easy to polish a car if you are having very little effect. So if you are going over an already shiny car with a very light polish, it's very easy if you are using the right technique and the right products. If, however, you have scratches that you need to wet-sand out, and then polish back using ever finer compounds so that you are left with a panel that has no sanding marks, and no buffer trails, this can be far trickier.
It's worth mentioning that there is a whole enthusiast community that loves polishing cars. While we're sure they enjoy the results, it's likely that part of the attraction is the process of polishing cars and the challenge of mastering the skill. There is a certain amount of art to it.