Why do you think that means anyone actually cares about those other countries? Applying a blanket rule as a starting point avoids having to single out the countries you actually care about at the outset.

Virtually our whole trade deficit is China, the EU, Japan, India, Vietnam, and Canada. Should we have just singled those countries out by name and grouped them together for purposes of imposing tariffs? Don't you think lumping Japan together with China like that would piss them off even more than tariffs would do anyway?