The reason why a writer might revise the second sentence to use passive voice ratther than active, is to emphasize or highlight the object that is being described.
Explanation:
For instance if the sentence is: A very famous paintor MichelAngelo sculped the statue of David in Italy. This sentence here is written in an active voice, because the action is located in the paintor.
If the writer wants to enphasize in the importance of the statue, because it is such an important and well known one, the writer could change from active to passive.
David´s statue was built by the famous paintor Michelangelo.
