Why does the game tell the player to move to the entrance upon successfully competing an adventure. What's the point?

When you successfully complete an adventure, you take the adventure card as a trophy.  The number in the green slot next to the game is a number of trophies associated with the card.  Because you have taken the card, you must move your character back to the entrance, because the adventure card is no longer in play.  If you were allowed to stay in the same slot, then you could assist for the next player who moves into that slot, assuming you haven't move out yet. 

The entrance is honestly a bad name for visualization.  Call it "The Lobby".  If you've ever been to the Met in NYC, it would be like that big lobby. 

yea when you play it makes more sense.  after you beat the adventure your character has to go somewhere.  if you need to visualize it, just visualize the lobby/entrance as the center of the musuem and all the rooms break off from it, so after each room is completed you need to go back to the lobby first to go to a new room.

So that the investigator is no longer available to assist other adventurers and focus dice for them.

 oops sorry guys did not see your replies as I was responding to  a  RSS feed that seems a bit slugish with its updates.