That’s like asking why a fair and just executive shouldn’t be interested in eliminating the overhead of an independent judiciary. Synchronically, it should. Diachronically, that’s one of the things that ensures that it remains fair and just. Similarly for transparency and leakers, though we usually call those leakers “sources speaking on condition of anonymity” or some such. (It does mean that the continued transparency of a modern democratic government depends on people’s continual perpetration of—for the most part—mildly illegal acts. Make of that what you will.)
Both can be true! This is essentially making it easier to do [x] argument, which itself is essentially security through obscurity.
It was always possible to do watermark everything: any nearly-imperceptible bit can be used to encode data that can be used overtly.
Now enabling everyone everywhere to do it and integrate it may have second-order effects that were opposite of one's intention.
It is very convenient thing, for no one to trust what they can see. Unless it was Validated (D) by the Gubmint (R), it is inscrutable and unfalsifiable.