I think it has to do with the majority of people who are affected not having much influence (money, power). I don't know if the "world response to this" is "so slow" or reporting of it is. I also don't know if it's the "world response" or that of the US that's being questioned. I suspect WHO were on this from the beginning, but there has never been a lot "the world" could do if it got involved.

The most effective thing that might have helped control the spread of the disease would have been people not touching the bodies of the sick or dead, or objects contaminated with their body fluids. Telling people they can't care for their loved ones or perform the traditional burial rituals obviously isn't that effective. It would have been more effective than anything else, but people first would have had to believe changing the way they did these serious and sacred things would have kept the sickness from spreading.