They only do that if you are a threat.

Lmao. Even CBP does not claim that. On the contrary, they say (and courts have so far agreed) that they can perform these types of border searches without any probable cause, and even without reasonable suspicion (a weaker legal standard than probable cause).

In practice they routinely do it to people who are friends with someone (or recently interacted with someone on social media) who they think could be a threat, as well as to people who have a name similar to someone else they're interested in for whatever reason, or if the CBP officer just feels like it - often because of what the person looks like.

It's nice for you that you feel confident that you won't be subjected to this kind of thing, but you shouldn't assume OP and other people don't need to be prepared for it.