This is essential in Scrum.
Why public? Well, so everyone can see and offer feedback on what are our team's biggest impediments.
Oh, and the list is prioritized. If the priorities are not obvious, then the ScrumMaster breaks ties.
And the real juice is that the SM is making sure the top impediment is always getting worked.
And there never comes a day when there is not a top impediment. (We never become perfect.)
Now, it may also be that the public impediment list reminds the SM (and everyone else around) why the heck we have an expensive person over there *not* doing "real work." (By the way, I think the SM easily pays his board by removing impediments. But you do the math. Of course, that assumes that the company culture does not stifle all the impediment removal efforts -- which has been known to happen.)
The exclamation marks in the title are there to suggest that way too often we find teams without a public impediment list.