I can see the problem.  It's called boredom.

Due to flight schedules, pilots are expected to wait around for hours at a time in airports until their next flight.  Airports are notoriously uncomfortable places to wait around, with chairs designed to be uncomfortable to sleep in, the lights are always on, constant announcements and your lucky just to find a television playing something other than flight schedules with audio enabled.

Leave the airport and you have to queue up for security searches on your way back in, and if it is an international flight you will have to clear customs in both directions which also takes time and a long time in queue.

For these pilots, a way to kill the time is to hit one of the ubiquitous bars near the gate.  One drink leads to another, which leads to another, as they kill hour after hour waiting around.  Sure they could eat, and they probably do, but in a 6 hour layover there's only so many meals you can have. Give them a place to nap.