I've listened to virologists and epidemiologists (i.e. "experts") being interviewed on television. The fact that the incubation period - the time between contracting the virus and initial symptoms appearing - is two weeks. This means that people with coronavirus will be "spreading it around" before they realize they're sick, so those individuals are likely to infect many more people. When awareness of this virus was first becoming evident in China, a [CDC?] virologist ran a simulation which predicted that "millions" of people would be infected. (I wish I could recall the source who conducted this simulation, but he claimed that statistics - to this point - are confirming the results of his simulation.) With each infected person infecting two other people, (during the incubation period), it won't take that many days for this to become a real problem.
Not sure about this, but wasn't the very first confirmed case of coronavirus in China reported in mid-January? (For some reason I seem to recall the first mention of this - in the media - around January 16th, but I could be wrong.) If coronavirus has been spreading since mid-January, (and each person who contracts it will spread it to two other people), I haven't done the math; but it seems to me that the number of infected people should now be fairly large.
Adding to this is the fact that there is not an effective vaccine. Dr. Anthony Fauchi - and other experts - are saying that a "safe" vaccine won't be available for [at least] 12 months, so the only effective way to fight this disease in the short run is prevention - as in washing your hands and wearing face masks.
Maybe (hopefully) this is not as bad as people are fearing, but there's certainly the potential that this could get a lot worse - especially if some of the more dire "simulations" turn out to be accurate. The fact that the stock market is dropping like a rock is an indication that the more gloomy assessments may be right. The big players on Wall Street have better access to information than you or I. It's their job to accurately assess the [financial] impact of events like this. (It's called risk analysis.)
When the "Masters of the Universe" are panicking and selling, it's an indication that we may have a real problem.