I agree on all points, but are restrictions on internal travel much different from restrictions on external travel? Seems to depend on the definition of the boundaries, and I think it’s hard to quantify the relative costs of external/internal travel restrictions. So I’m not sure what we lose by also restricting “external” travel other than another level of inconvenience.
For a country the size of the US? Yes, there is a MASSIVE difference between the two. The volume of movement by air between California and, say, Colorado is massively larger than that between California and China, and one of those places currently has a COVID-19 outbreak and one does not.
The distinction between the two for the sake of definitions is also very clear - whether the restrictions apply to travel that does not cross the borders of the United States. The currently-announced restrictions do not.
The question isn't of restricting external traffic in addition to internal traffic; we're only limiting external traffic. We probably need to be doing a bit of both, though with less draconian limitations on internal traffic to accommodate economic realities.
2. Isolation for those exposed or showing symptoms
3. Paid time off work for people who can't do their jobs in isolation, to make sure people report exposure and symptoms
4. Suspension of public gatherings
Some of these are being done voluntarily and/or by local governments, but that's very patchy.