How legal are sites/browser extensions that offer downloading videos from youtube, vimeo....?

Question

YouTube

For example, a website -- download a video, enter the url and we'll give you a direct link. For example, on youtube or vimeo. Or browser extensions. The question is why don't youtube, vimeo, etc. cover them up? Will they not sue?

Answer 1

The answer to the question in the title is simple: these tools are legal because they don't break the law per se, but those who use them to download videos that aren't under a creative commons license can do so. Now their actions are already illegal. Automatically, these tools by themselves violate only the terms of use of the services.
The answer to the question in the body of the question is also simple: any legal action costs money and effort, therefore any service whose terms of use violate any tool specially created for this, must, first of all, evaluate the ratio of damage from such a tool and the costs of doing so. to cover it up (by legal or engineering methods). If the damage is relatively small, then no one will bother. Plus, to prove the fact that the tool was created specifically to violate the terms of use of the service is not so simple.
So since we are talking about a possible violation of business interests, and not the law, everything is not so straightforward in the spirit of "stole - go to jail."