One of the major reasons for the ceasing of the Google Earth API would be browsers not making use of the Netscape Plugin Application Programming Interface (NPAPI) for security reasons. Chrome and Firefox did announce that they will no longer support the framework approximately two months back, and since Earth’s API happens to be built on this plugin, the cessation of NPAPI would result in the natural death of the Google Earth API.
Of course, with usage figures of the Earth API dropping drastically from 9.1% in September 2013 to a mere 0.1% in October this year, that too, played quite a factor. Google Earth API, you won’t be missed. [Press Release]