Because it's a common phrase? Same as "get carded"?

English is flexible; almost any combination of words can start to have meaning.

Tresspass is not a reflexive verb. It does not happen to you, rather it's an action you perform. Saying someone got trespassed is like saying you were driven when you go somewhere in your car, or that the door opened itself; you're taking the agency away from the person doing the trespassing and saying that they didn't actually do it themselves, but rather someone else did it/it something that happened to them.

This isn't a judgement on the article; it you don't want to say they were trespassing, then you should say it differently: they were _charged with_ or _accused of_ trespassing, etc.

> Because it's a common phrase?

I know it's a common phrase (albeit sa uniquely american one? Never heard this from e.g. Brits). I'm asking how it came to be that way when it seemingly makes no sense.

> Same as "get carded"?

No, because "being carded" (if I understand correctly) is something that does in fact happen to you. In trespassing, you are the one doing the trespassing (to something/someone else). That's why I find it so weird that Americans turn the subject into object in the sentence.

> English is flexible; almost any combination of words can start to have meaning

Sure. But taking a perfectly fine sentence and turning the subject into an object (when the physical reality is unchanged) seems strange, and warrants curiosity.