I was coming here to ask this exact question. There's no reason it makes sense to search electronic records at a border crossing. As you point out, the point of the search is to control customs and ensure there's no smuggling going on. But electronic records are not smuggled physically. There is zero reason to do so.

So the actual reason customs agencies perform these searches is that they are allowed to do so because of the way the laws are written and precedent is set.