Why wasn't the USGS able to reach anyone to warn them?
No pre-existing network. These things don't work unless you have a defined network where the people have already met to set up procedures.
Otherwise you're either lost in the immense bureacracy of countries like Sri Lanka or India trying to find someone with the authority to order an evacuation (mind you, the people you're calling have never met or heard of you....if you were them, would you believe them) or you're somehow trying to call the local police departments in the areas in question.