The companies providing the APIs don't have to justify the "why". When I was working on Facebook applications a few years ago they would change the API calls and rules almost monthly, app developers had to adapt or die. The changes were often due to apps abusing the system in one way or another, but Facebook defined what was abuse or not. Sometimes the changes just looked completely arbitrary and sometimes meant that some applications were just not possible anymore due to vanishing API calls.

Exporting the private data from Facebook is considered a big no-no, from what I remember the TOS might only allow you to do so for a short period. Maybe that search service gets away with it because it stores an index based on the private data and not the private data itself. If Facebook gets uneasy with how close the index is to the original data or what private information leak might happen if Greplin is compromised, that could be a good enough reason to put a stop to it. Facebook not getting into a private information leakage scandal is probably more important than allowing a startup to live on Facebook data.