Because everything he did was completely out of character, and the manner in which he died was completely contrived. Then, just to add insult to injury, none of his friends and crewmates for the last ten years really seemed to care all that much.
How was it out of character? That's the part I'm most confused about. And Archer and T'Pol definitely seemed to care during that scene in his quarters. I will agree that it was contrived, but it sent a message of honor, loyalty and nobility and I forgave it as a result. I mean, the deaths of Spock and Dax were contrived as well, but those are forgiven.