https://www.cdc.gov/ebola/situation-summary/returning-travel...
But, you're ignoring that it's also not exactly a blanket ban on travel from the DRC, just "within the last 21 days", which... does that make a meaningful difference? And, where are the other western countries doing the same? Kinda my point. If it's done at all, it's a day late and a dollar short.
[Edit: Arodex notes that it can remain dormant for years (at https://news.ycombinator.com/item?id=49418182). So, yes, someone could bring it back. It probably wouldn't be an active infection, though. But what is the alternative? Nobody who ever visits the DRC can enter the US ever again? That seems like overkill.]
What's the alternative here though? It's not really okay to lock your own citizens out of the country indefinitely, so there has to be some way for people to be able to come back home eventually. Requiring an Ebola test on entry would be one option, but those Ebola tests would probably be better used on patients in Africa, so it would be hard to defend such a policy from an allocation of resources perspective.