Brees isn't the same as the players I've mentioned. Paying QBs like Brady, Rodgers, Brees, Wilson, Ryan, Rivers and Luck makes sense, since they are good enough to justify their hefty contracts. Foles was surrounded by the best o-line, best d-line, one of the best defences in general, a great receiving core with Ertz, Jeffery and Agholor, a good RB committee and excellent play calling. He obviously had to play well, too, but I'm fairly sure the Eagles are happy to start with Wentz again. Point is, that it makes no sense for the Giants to trade for an average to decent QB, who will earn quite a bit, if you can get the same from a rookie QB on a better contract for your team, while being able to go after better player in free agency, since you have more cap space.