You got one correct answer to the question asked, which is "why". And it has nothing to do with AI. This has been a thing on websites for 20 years - not many, but some. They use javascript to choose what to copy to the clipboard. As others noted, there are ways around it.
For the why? Well, to try and prevent precisely what you were doing.
There are ways of making it more difficult (impossible for the average or lightly-teched user) to save/copy images, for example. Some sites attempt to do that.
It's all a matter of trying to protect what they've published. Which is certainly legally their right. But is also pretty easy to get around - at least on desktop. I haven't had to bother on mobile, myself.


