Do you know what a scientific model is? It is a set of equations basically that states the predicted outcome of a theory or hypothesis, you know an educated guess. Scientists create theories and hypothesis and then design experiments to control variables and measure the outcome. Different scientists have slightly different models for this virus spread.
Epidemiologists/virologists have theories and hypotheses about how these viruses spread. You can run the model's equations through a computer and keep changing the variables and parameters to see what will happen.
Right now it is a real time experiment that I dont think has ever been seen on this scale. The globe has never been on lock down, stay at home, hardly any air travel or even state to state travel, ever I am pretty sure. Since there is really poor testing and data there can be incomplete and inaccurate data going into the models, like, infection rate per infected person in a crowd of a certain size, data on how virulent the virus is, etc etc.
So the various models/sets of equations are pumping out results daily and getting tweaked daily to modify the parameters. Very few people are going to be right from their first estimates on March 1st and if they are it was a very good guess.
And I suppose after the all the study and theories and models on tornadoes, volcanoes, earthquakes over the years you are pretty upset that these damn scientists cant even predict when one will happen.