The expansion of the coronavirus is not a joke and various precautionary measures are needed and necessary. That applies to gaming events such as GDC as well.
Sony and Oculus have already announced that they are pulling out of GDC and now Kojima Productions is following their footsteps. Here's what their message says: "Kojima Productions has made the difficult decision to cancel our participation at the 2020 Game Developers Conference due to increasing concerns related to coronavirus. Although much-anticipated, unfortunately, this cancellation also includes Hideo Kojima's session on the 19th and Eric Johnson's session on the 16th". A brief yet clear and understandable decision. Let's hope that the situation gets at least somewhat better in the near future.
GDC 2020 will begin on March 16.