Sometimes the experimental drug has unexpected side-effects or is less effective than the placebo. Both sides of the trial are a gamble. It is a trial because

Sometimes the experimental drug has unexpected side-effects or is less effective than the placebo. Both sides of the trial are a gamble. It is a trial because literally nobody knows for sure what the outcome will be -- only an informed guess that the new treatment is a good idea. When trials are extremely effective, they are sometimes halted and rolled out early. That sounds like exactly what Pfizer is attempting to do here. The company thinks that they have a clear-enough signal to be worth going to the press and preparing FDA for the EUA. Pfizer will have made an embarrassing error if the final trial-results turn out to differ with their claims, but if they don't, then Pfizer has given a several-week head start to rolling the drug out to all patients.