Irdeto, the developers of the anti-piracy software Denuvo, announced a new tool that will allow game developers to easily track leaks back to its original source.
So if they watermark, then this may become an issue. If you buy a game over steam for the purpose of leaking, steam or some payment provider knows your bank account. From that you can be traced down.
So to hide, a cracker would need to have a fake bank account, or live somewhere lawless like in Russia.
Watermarking isn't to stop you from buying a game on steam and cracking it, it's to stop you from uploading screenshots or videos of a game you have alpha/beta access to.
If a game does ship with this, it's also shipping with denuvo. A cracker that can bypass denuvo can bypass the watermarking too.
According to the article this is a watermark for the game file. Which could be hidden by modifying certain parts of the game in a way that functions the same but results in a unique file for each copy distributed. (Similar to adding a unique pattern of double spaces to a word document.) Without knowledge of the watermarking algorithm a leaker couldn't be sure the watermark has been removed/obscured.