I feel like it is a set of political battles that the US Treasury Department doesn't want to fight. Americans have been stubborn with how they use their currency. The last major push was trying to replace the dollar bill with the dollar coin and that has been a failure.

The remaking of American paper currency to be in line with the rest of the world will likely spark a massive political storm, including potentially replacing the people and places depicted on the currency. It would also mean re-educating the population on what the currency should look like.

The current $100 notes do a good enough job.