It is generally understood that when Barabbas was released from prison, he was not required to return after the Passover festival. Why believe this was the case? Perhaps a more modest temporary release of a prisoner makes better sense of the poor external attestation of such a practice (historicity of the paschal pardon discussed here: Is the story of Barabbas possibly fabricated?).
- Permanently releasing (presumably any, given that Barabbas was a murderous insurrectionist) a prisoner at crowd request seems implausible.
- A temporary release at crowd request provides accountability. If the released prisoner acts up, everyone would know the Romans will punish both the prisoner and people at-large harshly.
Given public support for Jesus on Palm Sunday, perhaps Pilate thinks he can play the masses against the Jewish leaders. Mark stresses that the Jewish leadership plotted to convict Jesus in secret, and there is no popular support for Jesus's conviction (Mark 14:1-2, 48-49).
If the masses show support for Jesus, the Jewish leaders will have a hard time disposing of him. The Romans would be reluctant to crucify a popular figure who broke no Roman law, and the masses would rebel against the Jewish leaders for instigating a judicial murder against their beloved teacher.
Some uses of the word "release" (ἀπέλυεν and related forms) seem to connote finality, but I don't know if that's necessarily the case (https://biblehub.com/greek/630.htm).