First is the "why now" question. I don't know, but let's hope the MSM asks. That said, it appears at least tenuously connected to Black Lives Matter issues.
And, Francis Scott Key's song has plenty of room for fodder here.
First, as The Intercept notes, the third verse salutes the killing of slaves. Or rather, slaves attempting to escape to the British vessels that bombarded Fort McHenry and led to Key's words.
But, other people have other reasons to balk at the song.
The fourth stanza, per Wiki, is explicitly Christian, claiming America's motto is "In God is our Trust." And, now you know where Salmon P. Chase was inspired to inscribe our coinage in 1864; "In God We Trust" likely started with Key.
Update: Per Yahoo, Drew Brees, I "get." (I don't "accept," though, especially as Kaep had already said this isn't anti-military.)
Richard Sherman, with:
"At the same time, you’ve got to honor your country."
Still gets it half-wrong, as I see it.
That's just the old "my country, right or wrong," in new dress. And, it's kind of surprising coming from him.
(And Jerry Rice [Tap-Dancing with the Stars?] has reportedly now taken the Sherman fade route.)