Wendy Sherman is an amazing diplomat and probably has a better chance than anyone at fostering legitimate dialogue and increasing understanding (for what it's worth, she accompanied Madeleine Albright on a trip to DPRK in 2000 in which they met with Kim Jong-Il and was an instrumental player in the Iran nuclear deal negotiations).... Despite the fact that Beijing seems to be hardening its line against the US and potentially believes it is in an inevitable existential conflict, diplomats in Washington probably feel a responsibility to continue attempting to engage to show that there is good faith on the US side. Obviously the US is much less monolithic in it's foreign policy approach than the PRC is, with differing opinions on how best to engage/compete, but good faith efforts are important at showing the rest of the world that we're trying to make even the difficult relationships work - the PRC is providing a very different image of combative intransigence that makes even the most competitive US policies look somewhat accommodating.