Answer:
Everything was too hot.
Step-by-step explanation:
According to the Big Bang theory the entire universe existed in a dense singularity i.e., a location where the gravitational field is infinite. The material inside the singularity started to expand due to quantum fluctuations.
After the expansion stage had started everything was very hot and atoms could not form. But after this stage which was about 380,000 years after the Big Bang there was a cooling effect that photons could travel and reach our eyes.