Because "trade war" is not the complete end of trade any more than "world war" is the complete end of the world or "guerrila war" means all silverbacked simians are destoryed.
No one claims that "trade war" means "end of all trade." That's just stupidity.
"Trade war" is a general terms that applies to increasing tariffs, usually tit-for-tat, between two countries. Folks use it in a wide range of situations and it is not some precise term of science, but its general meaning is well understood and only a dishonest pedant would try to pretend it means "total end of trade between two countries." Here's some easily searched definitions:
trade war ˈtrād ˌwôr/
noun noun:
trade war; plural noun:
trade wars
- a situation in which countries try to damage each other's trade, typically by the imposition of tariffs or quota restrictions.
A
trade war refers to two or more states raising or creating tariffs or other
trade barriers on each other in retaliation for other
trade barriers.
Even Drumpf himself called it a trade war, mentioning they are "easy to win."
It's just silly to pretend that "trade war" involves eradication of all trade. That is not the meaning.