When Lincoln was alive, it was considered bad manners to wear a hat indoors. He's just being polite
Did you by any chance also see Socrates, Billy The Kid, and Freud running through the food court?
There is (was?) a pizza parlor in Santa Clara county CA that named all the tables for famous (or infamous) people. Of course they had a John Wilkes booth.
Do you think he actively avoids those, or was this just the most convenient seat at the time?