What's the long term gain? It's just a unit of measure, ultimately arbitrary. Standards bring efficiency, and we already have a standard.
Exactly: the entire world has a standard, and the US is doing its own weird thing.
The long-term gain is being able to sell your stuff to the rest of the world, and being able to import stuff from the rest of the world without paying a Weird Format Tax.
Would you rather manufacture stuff for 8 billion people, or for 340 million?
Maybe avoid to crash half a billion $ probe on Mars surface?