That requires you to click into all of the ones you don’t want to unfollow, in order to unfollow all of the ones you don’t want to read. It’s just as much work or more than clicking into the ones you don’t want to follow to get to the control. If you don’t have time to read them all you can’t ever get to the dismiss button.
When you have 10 in your list it might be fine, but when you have 200 it’s a huge pain.
Instead of clicking on and having to read through 100 threads of 200, I could just click a stop tracking control instead.