To shed some lights on why power sliding is so unreliable, doing so requires to be familiar the surface on which you’re attempting it. Being familiar with it means that you basically failed to and fell down multiples times before getting it right, which already requires a good skill level.

And you cannot assume that power sliding on a surface will be similar to another one that looked the same because a slight change of humidity, dust or grease may totally change the outcome and transform the slide into a hang up that will throw you at the floor pretty hard.

So if you combine a really thin margin of error with the inability to confidently execute it on new surfaces, it makes powersliding a pretty unreliable way of braking unless it’s an emergency, in which case jumping off the board is much easier.

Meanwhile, you can power slide at will in the skate park because you know the surface by heart, and it’s easy to get it consistent by how many times you just rode it.