I take the word "notorious" (ἐπίσημον) as important here. It is also translated as eminent, notable, and infamous. These adjectives could also apply to Jesus. Since we no of no other famous prisoners, it stands to reason that Jesus and Barabbas were the two most famous prisoners. Jesus was known as teacher, healer, and recently as a man claiming to be the Son of David who overthrew the money changers tables in the temple.

I take the word "notorious" (ἐπίσημον) as important here. It is also translated as eminent, notable, and infamous. These adjectives could also apply to Jesus. Since we know of no other notable prisoners, it stands to reason that Jesus and Barabbas were the two most famous ones. Jesus was known as teacher, healer, and recently as a man claiming to be the Son of David who overthrew the money changers tables in the temple. Barabbas was known as a leader of an insurrection against Rome. Both were accused of trying to overthrow Roman rule, although in Jesus' case, his understanding of the Messiah's role did not involve violent revolution.

So we may conclude that these two names were brought forth because they were the most famous supposed revolutionary leaders who were in prison at the time.