Having travelled through Palma Airport many times, I'm really not surprised that there is a fall in sales - as so much time is wasted in queuing. We always arrive around 3 hours before the flight home as we know we have to join the dreaded queues - to park, to check in luggage, for a drink or food, security checks, passport control and finally the long trek (who planned that?) to the departure lounge before a final queue to get out to the plane.
Flying used to be quite pleasant, with a time for a drink and a little light retail entertainment before the flight home. But I think most people are reduced to just looking longingly at the shops whilst stuck in the queue.
I'd love to have a last shop at the airport, but sorry I'm too busy queuing!