It wasn’t just to show Cersei but everyone including Dany. But these casual fans that don’t know the difference between a wight and white walker always got something to say. If they don’t go to capture a wight Dany never sees herself. Then she would keep fighting with Cersei. The north would be the only ones fighting the dead. Then they would get added to the dead army and by the time Dany takes the throne. The death comes and wipes her army and dragons out. Night king wins then. Now sure he has a dragon now too but at least everyone aware of the threat.