There used to be a time when it was just accepted that most of the good conferences/gatherings would be in the US, and it would either be important to go to, or be relatively straightforward to reach and attend (especially for Canadians), and nobody would think twice about it.

Now you have some very talented/consequential people just refusing to visit the country. Regardless of any qualms about the "content and logic", this should set off alarm bells for any American. Plus, this would've been a whine if he'd complained and had gone anyway. But he is not going, and has explained his decision. That makes it more of a statement.

I think the title is appropriate and is probably meant as a double entendre. The US does seem to be declining in many ways. Personally, visiting the US under the present government just feels too risky, they seem really hostile to foreigners.

The whining you hear is you.

Its pretty clear that "declining" has two different and, I would agree, apposite meanings.