Somehow GDC itself still isn't cancelled.
Amazon AWS GDC 2020

Two more companies announced today that they are cancelling their GDC 2020 plans over fears of the coronavirus (COVID-19). Earlier today, Amazon announced that they would no longer be headed to the latest installment of the annual event.

Amazon said that they would host a "global online event" to share news about what they were going to show off at the conference. This is actually similar to what other companies have planned in the wake of them cancelling their GDC appearances. Just yesterday, Microsoft said that they would also have digital-only event to showcase what they were going to show off and talk about at GDC.

To our friends across the industry,

AWS has made the difficult decision to withdraw from the 2020 Game Developers Conference (GDC) in San Francisco due to continued concerns over COVID-19.

While we won’t get to see everyone at GDC this year, we still have exciting things to share. AWS Game Tech has decided to host a global online event, open to everyone, to showcase our planned content for GDC and more.

Look for more details in the coming weeks. Click here for early info.

We’re all part of such an amazing community. Thanks for everything you do.
Just minutes ago, Blizzard also announced that they were no longer going to GDC 2020. The announcement came via Twitter and once again cites the ever growing concerns over COVID-19 as the reason for the change in plans.

"Blizzard will no longer attend this year’s @Official_GDC due to growing concerns related to COVID-19. The health and well-being of our teams is our highest priority.

"The conference is and has always been an important event for our developers, so we look forward to participating in the future."
With these latest cancellations, Amazon and Blizzard join numerous other companies that have cancelled plans due to fears about the coronavirus. Many of these companies have pulled out of GDC appearances, various fan events, tournaments, or other prior obligations.

So far, the companies we know of that have cancelled their plans include:

UPDATE (3:48PM ET): Certain Affinity also just announced that they are cancelling their GDC plans. Certain Affinity has helped work on games like Left 4 Dead, Halo: Combat Evolved Anniversary, and even Call of Duty: Modern Warfare Remastered to name a few examples.