>>Probably another attempt to isolate themselves from the "World"<<
True. But someone told me that a most likely reason is because the WTS really doesn't like their publications to be "remembered".
As a publishing company, what the WTS fears the most is her own publications. ISBN cataloging also subjects published work to archiving, such as the Library of Congress and other mega libraries around the world. Whatever the WTS prints today she will have to hope people will forget about tomorrow, or worse, hope she doesn't have to defend or explain a reversal or answer criticism that she is regurgitating the same old material over and over again!