Specifically if we don’t think the effected country actually has the resources to do so. The alternative is wide spread contagion - take swine flu and bird flu, both started in China, and yet the lack of any monitoring allowed them to spread around the world before being contained. In that case the outbreak was deliberately not disclosed, but choosing not to disclose and not having resources to disclose have the same effect for /other/ countries, including your own.
Things like where a disease has spread is important to work out the risk of it reaching your own country.
You do know that most of what the cdc does is monitor right? It’s not actively going out to spend Your Tax Dollars treating patients - that’s something that the US doesn’t even do in America.
Alternatively we could choose to not track outbreaks and just hope that Ebola knows we’ll deport it if it comes here. (That works right?)