One of the problems is that the US president has certain actual powers, and ignoring him doesn't work for things he actually has the power to do.
One of those powers is to direct federal agencies as to the official names of things. That doesn't force *the rest of us* to call things by his new names, but it does mean that federal agencies will call them that in official communications and on maps, etc.
His power isn't unlimited, but it's not nothing, either.