Why does hobbes's version of the social contract give absolute power to a sovereign?

It gave absolute power because he claimed that governments formed out of numerous individuals would inevitably cause countries that behaved as anarchically as the individuals did without a contract. For that reason, it is necessary for there to be a strong individual ruler who is above the idea of state and who is capable of protecting the state's interests from foreign incursions or warfare with foreigners. If a country didn't have such a ruler it could easily start wars with other countries and would soon fail.