"As with the first game between these two masters, no annotations are required because it is obvious that Jaffe did not make any attempt at winning, and his blunder on the twentieth move is best concealed and the game passed over."

The first game:

But isn't it more likely that those who were there, including Capablanca and Hermann Helms (and possibly Marshall), had local information that Jaffe had indeed thrown one or both his games against Marshall to deny Capablanca his fairytale return tournament victory in his home city Havana?

After all, as Hooper and Brandeth point out, it was due to Capablanca's graciousness in offering to play Charles Jaffe and Oscar Chajes in a match, which was changed to a mini-qualifying tournament, that Jaffe was even in the Havana 1913 tournament:

"52 Charles Jaffe - JRC. New York, 18 October 1912. Both Jaffe and Chajes, two of the Capablanca leading players of USA, felt aggrieved that they had not been selected to play in the Havana tournament of 1913. To settle the question Capablanca offered to play a match of three games against each of them. Shortly afterwards a qualifying tournament was arranged instead [i.e. a tournament in which Capablanca, Jaffe and Chajes would play three games against each other.]. Jaffe finished his match, but Chajes chickened out after one game." (Hooper, D. & Brandeth, D., "The Unknown Capablanca," Dover, 1993, p.55).

This is not the gesture of a vindictive prima donna, still smarting over his loss to Jaffe eight months before. Rather it is the gesture of a true sportsman, willing to put himself out to help Jaffe play in the Havana 1913 tournament.

Also Marshall himself would have then been more influential in American chess than Capablanca was and he would not have stood idly by and allowed Jaffe to be unjustly persecuted by Capablanca over a game Jaffe had played with Marshall, unless Marshall himself agreed with Capablanca that Jaffe had probably blundered his queen on purpose to deny Capablanca victory.

"Why, if Capablanca was so good to Jaffe, would Jaffe repay him by throwing his game(s) against Marshall to help the latter win the Havana 1913 tournament over Capablanca"?

One answer is suggested by a comment above, that Jaffe "could give amazing odds to a Patzer." It seems that the impverished Jaffe was a gambling man, and he would no doubt be able to obtain very good odds in a bet that Capablanca, who had defeated Marshall comfortably in their 1910 match, would not win the 1913 tournament in Havana his home city.

Like most hustlers in any field, the tendency is to look almost always to the future, towards aggressive action, and at any weakness in their mark/opponent, with little if any regard to their own deficiencies, regardless of how clear they might be.

That is vividly clear in this game and "hustler blindness" surely would hurt one playing against Marshall.