Comment by swatcoder

The incentive for commercial providers to apply watermarks is so that they can safely route and classify generated content when it gets piped back in as training or reference data from the wild. That it's something that some users want is mostly secondary, although it is something they can earn some social credit for by advertising.

You're right that there will existed generated content without these watermarks, but you can bet that all the commercial providers burning $$$$ on state of the art models will gradually coalesce around some means of widespread by-default/non-optional watermarking for content they let the public generate so that they can all avoid drowning in their own filth.