I dont understand why people like a journalist working on things they dont want seized would carry this kind of data on their device at a situation like this (border crossing), I see it as more useful to remove that kind of data from the device first.

Probably because everything seems to be an "app" these days. Even when it has no business being one.

Because you may need the data in the data during/after your travel and lack clean way to access safely, securely and anonymously remotely.