I disagree: enough people use youtube-dl and Invidious so Youtube’s legal team actually bothered to reach out to those projects. Let’s take a look at some stats:

• Invidious has 11k stars on their GitHub page https://github.com/iv-org/invidious
• NewPipe has 24k stars https://github.com/TeamNewPipe/NewPipe
• FreeTube (desktop app for Youtube that could either use Invidious API or scrape Youtube itself) has 7k stars https://github.com/FreeTubeApp/FreeTube
• Piped has 4k stars https://github.com/TeamPiped/Piped
• Piped also gives some stats about its userbase here https://github.com/TeamPiped/Piped/wiki/Instances — over 173 thousands of registered users on the main instance!
• youtube-dl is one of the most starred projects on Github
• And all of the projects above have lots of forks