I don’t see any realistic way it could have been kept out of the country, especially in light of selfish idiots like that female in NH who KNEW she was infected and instead of staying quarantined, went out to a social event anyways.
I don’t think the goal of travel restrictions is to keep the virus out of an area, just to slow it’s spread. Slowing it even a week or two could buy time for preparation, to processes and plans nailed down, how to handle outbreaks so you don’t end up with sick first responders and healthcare workers.
Any slowing helps the healthcare systems.
We bought some time when we stopped planes flying from Wuhan but needed to keep expanding it to endemic areas. It’s not something you can do halfway if you want it to work.