Notice the opening times: 10am to 9pm. Barcelona shows tend to be busy from opening time till about 1 or 2pm, then they slow down as the public, and many of the dealers, take off for a looooong lunch break. Starts getting crowded again around 5 or 6pm, until 8pm or more. At 10pm, after many people in other European countries have already gone to bed, the Iberians start thinking that it might possibly be time to start thinking about dinner. (Don't even bother to go to a serious restaurant before the show closes at 9, because the chef isn't serving anything yet.)
