Throughout the play, Rosencrantz and Guildenstern never leave the stage. What stops them from following the Queen's attendants to go find Hamlet?

Before they can leave the stage, Polonius enters, and they stop and bow to him. Polonius nods briefly and hurries to Claudius. Rosencrantz and Guildenstern look after him and overhear Polonius tell Claudius that the ambassadors from Norway have returned.