For reference, here's the chart: https://en.wikipedia.org/wiki/File:SE2017Aug21T.png
Such as the fact that that word refers to the USA and not the whole of the Americas :)
It is a little tongue-in-cheek, but I find it amusing that the history of the word itself is an example of what it describes.
History is overflowing with perpetual name changes for countries, regions, cities, etc. There's nothing unusual about it other than that in this case it applies to the US, which as the sole superpower is a magnet for over-inflating such ridiculous non-issues.
America is on the down-slide of greatness. You can tell this by taking an honest look around, but also just by listening to the widespread shrill insistence on how great it still is. So "Great American This" and "Great American That" is not only played-out as I said, but probably inaccurate as there become fewer and fewer great things to be found in America.
Anyway. The phrase "Great American Eclipse" also sounds just a tiny bit like America is taking credit for the eclipse, when of course the eclipse didn't need any help from America. America just happened to be underneath it this time around.
Finally it reeks of the same old American self-congratulation (for things that are not at all unique to America) that you can see almost anywhere in America, including your comment, patronizingly reminding me of my rights.