The Public Health Department of Santa Clara County has issued a mandatory/compulsory order which bans all gatherings of more than a thousand people.
The ban starts from March 11th 2020 at 12:00 a.m. Pacific Time and will end after three weeks till 31st March. This mandatory order was issued due to the outbreak of Coronavirus. According to the government website, there are 45 confirmed cases of Coronavirus in the Santa Clara County region and there has been a death of one person due to Coronavirus. The Santa Clara County region includes cities like Cupertino, San Jose, Mountain View, Morgan Hills, Los Altos, etc where most of the tech companies are located. Public Gatherings may help in the spread of Coronavirus (COVID-19) which is why the Public Health Department of the Santa Clara County issued this mandatory order.
Even before this order was issued, Google had already cancelled its developer conference, Google I/O for which the amounts of the tickets would be refunded. Facebook also cancelled its F8 developer conference due to the Coronavirus outbreak. Not only these two companies cancelled its events, but the Mobile World Congress (MWC) was also cancelled due to Coronavirus.
Read the full statement here:- https://www.sccgov.org/sites/phd/DiseaseInformation/novel-coronavirus/Pages/order-health-officer-03092020.aspx