Vienna Palace, after the letter to Maximilian was sent out, Franz no longer paid attention to the issue of Mexico.
There have been many recent events, and the Prusso-Russian War had tied up too much energy. John Bull wasn't staying quiet either and had started causing trouble on the African Continent.
Seeing France and Austria aggressively expanding, they could no longer sit still. Hindered by the rebellion in India in the previous years, the London Government didn't have the resources to come and create issues.
Merely relying on civilian colonial teams was obviously not competitive against France and Austria. A colonial team of a few hundred perishing on the African Continent is nothing out of the ordinary.
With France and Austria having gained the upper hand, they both trained their own enforcers. Recently, in the Zimbabwe region, Anglo-Austria encountered armed conflict, and then thousands of black men stormed into the South African colony, turning the place upside down.