The reason this is so important and so necessary is that of all the Executive Branch departments, the State Department BY FAR has the worst form of a cultural illness where its employees lose sight of the fact that they serve the American people and they instead believe they serve whatever nation or cause their diplomacy is focused on.
If you ever served downrange in the U.S. military and had to work closely with State Department employees, you know I speak truth.
Bravo, Mr. President and Secretary Rubio. This change is wholly necessary. Symbolism matters.
And if you are a State Department employee and don't like this?
Then quit, and good riddance.
The US State Department lobby used to display the flags of the roughly 200 countries with which the US maintains diplomatic relations. Now, it displays 200 American flags, to remind State Department employees who they work for.