I don't believe anyone is saying every single person coming into the US will get searched. We _know_ they are not. But searches _do_ happen and _are_ legal, and that alone justifies preparing for the eventuality.
My employer has always had rules about how to take care of data on your devices. They tell you to enable encryption and to never leave your company laptop alone and stuff like that. The vast majority of employees will never have their devices stolen, but the fact that some might is enough justification to make sure everyone does their best to protect their data. It's the same thing.
That you always had very easy experiences with immigration _is_ the anecdote here, because it does nothing to change the fact that _some_ people will get their devices searched (and data potentially copied) by Immigration agents.