Fr example, I can use "Mute Site" to turn off the sound of all the videos from a news site so I can read the news pages w/o bothering people around me. If I have only "Mute Tab", I have to do it every time I visit the website. Also, if it's a pop-up window, I don't have a tab to mute it.
After starting this conversation I researched further and can see the utility of the Mute Site option. I see that it was started from Chrome, so that may be part of the reason it hasn't made it to Microsoft Edge Insider Builds. But if enough users request it, it is likely to be included.