I think people are rejecting the New Sincerity because they believe that what is sincere must also be trite: greeting cards, for example, have destroyed all meaning to the phrases "Happy birthday," "With sympathy," and etc. The most important occasions call for (now) the least sincere sentiments. And therefore the most trite.
But sincerity is (truly) the opposition to the trite, the frivolous, the meaningless. Sincerity has money down on this game and it's not taking chances. Sincerity recognizes an investment in poetic communication that is emotional, honest, and less interested in being smart than being true.
Isn't New Sincerity really just the end of hiding behind all of our neurotic, cooler-than-you bullshit?
I've been photographed naked. I'm a New Sincerist.