Their reason for doing so is that they're evil. (That's the motivation).
The proof that they're evil is that they do it. (That's the context).
Though, truth be told, at least some of the commenters object.
Also, such allegations, standard antisemitism as they are, aren't directed only ever against Jews. Remember how throughout the 1990s we were assured the Western sanctions against Saddam's Iraq had produced precisely 500,000 dead Iraqi children, a number that didn't rise as the years passed? Remember how after the American invasion of 2003 nary a single bereaved Iraqi mother was ever produced for the cameras?
Then again, to a noticeable degree, anti-Americanism and antisemitism are related these days. They're aren't the same, not even twins or siblings, but they're easily cousins, the two phenomena. Why, even the column cited here has its anti-American undertones.