When specific cities have spikes/surges within a state isn't there still free travel in and within? So spreading is inevitable isn't it?

Yep.  However, the economy of some places depends heavily on tourism.  Therefore, those places are never going to isolate themselves.  Money is just too important.  Worse, many people in high infection areas flee to areas of lower infection to escape the virus - and take it with them.  If they really want to beat this virus, they need to isolate states and counties within the states (and some cities) for 3 weeks.  But this is america and people here won't stand for anyone telling them what they can and can't do.