with our flight systems, can we not pretty readily track anyone flying OUT of that area
Because your (USA's) flight systems extend as far as the origin points of flights that terminate in your country. What happens outside that, you're dependent on other countries (or the traveller themselves) reporting information to you. (Of course, the NSA are probably perfectly well aware of the full flight history of anyone leaving the area, but they can't admit to that without being jailed.)
Better than have it reach pandemic proportions
It may have reached that point already. The WHO are expecting that, by Christmas/ New Year (when there will be a global surge of travel, intranationally and internationally) essentially every country in the world will have had several cases arrive from West Africa (albeit via third countries). The likelihood of secondary cases from those primary cases is high ; whether there are then tertiary cases is going to depend on local responses.
Which doesn't mean that we're fucked - just that global vigilance is going to have to increase and efforts at containment will have to increase rapidly too. So ... maybe every international airport in the world is going to need the nearest hospital dedicating to isolation cases. And if that means that no operations which are not urgent get carried out in the remaining hospital beds, then that may be the price.
For what it's worth, it's plausible that the number of deaths from the economic disruption caused to the three core countries is already exceeding the number of deaths due to the virus.