Depending on how spread goes, it would be easier to ban internal travel after banning international travel than going 0 to 100% ban in one swoop. Don’t underestimate that the damage of social unrest can easily surpass the potential damage of the virus. Remember public policies deal with people with emotions, not robots.

This would make more sense if the travel ban was bidirectional. But as you said, a lot depends on how things are progressing, which we don't actually know in the US due to poor monitoring. Which is why I said it's not clear if this is a step that will make any significant impact, although to your point it might work as theater either way.