It seems like a low chance and high risk.

Low chance, certainly. Less than 30 of 10,000 RAF prisoners successfully escaped to Britain or neutral territory during the war. Recapture was almost inevitable but risk of death was, until the Great Escape, relatively low; up to that point Germany had broadly adhered to the Geneva Convention (for western Allied prisoners, very much not the case in the east) as outlined in [a US War Department pamphlet] (http://www.lonesentry.com/manuals/captured-rights/index.html): "If you attempt to escape and are recaptured, you are liable only to disciplinary confinement not to exceed 30 days." The execution of most of those recaptured after the Great Escape was a war crime, and prosecuted as such after the war.

As to what they were trying to accomplish, Roger Bushell, "Big X" at Stalag Luft III and the basis for Roger Bartlett in the film The Great Escape, said "The only reason that God allowed us this extra ration of life is so we can make life hell for the Hun". By 1943 there were 400,000 German soldiers involved in guarding prisoners of war, and after the Great Escape another 60-70,000 auxiliary troops became involved in the hunt for the 76 escapees. The line in the film is: "... it is the sworn duty of all officers to try to escape. If they cannot escape, then it is their sworn duty to cause the enemy to use an inordinate number of troops to guard them, and their sworn duty to harass the enemy to the best of their ability." It was about the only way POWs could play some active part in the war (that, and gathering information to pass back to their own side via coded letters).

The film isn't entirely accurate, though, unsurprisingly; it wasn't a sworn duty; the RAF pamphlet "The Responsibilities of a Prisoner of War" is almost entirely concerned with not giving information away and barely mentions escaping. Some POWs, like Bushell, did their utmost to escape or cause trouble around camps ("goon-baiting"), but they were a minority. Michael Walzer in "Prisoners of War: Does the Fight Continue after the Battle?" concluded: "The fight does not continue after the battle, not for the men who have been captured, unless they choose together to fight on and accept the risks that choice involves. They have every right to choose differently, and this is what most of them do, opting for benevolent quarantine whenever it is offered". The derring-do of escapers makes for exciting stories, and became the dominant popular perception of prison camps after the war with memoirs like The Wooden Horse and The Colditz Story and associated TV and films, including of course The Great Escape, but "life for POWs who were interned in German camps was mainly composed of boredom, frustration, hunger, cold"; as an ex-POW put it "fictional portrayals of POWs have invariably focused on the excitement generated by attempted escapes, gloomy resignation and stifling boredom more typically characterized a prisoner's daily existence". S. P. Mackenzie's The Colditz Myth: British and Commonwealth Prisoners of War in Nazi Germany presents a fuller picture of the average POW experience, a [2004 article from The Independent] (https://www.independent.co.uk/news/uk/this-britain/the-great-escapes-the-harsh-reality-and-true-heroism-behind-the-hollywood-prison-camp-epics-535215.html) gives a few snapshots ("This business of it being our duty to escape has been greatly exaggerated").

Post-war accounts also overwhelmingly focus on officers and senior NCOs, who could not be obliged to work under the Geneva Convention; other ranks had rather different experiences, each having its own perils: "Officers and non-working NCOs, feeling cooped up and bored to distraction, might envy what they imagined was the comparatively varied and incident-filled life led by working prisoners. Those who had no choice but to labour often saw things rather differently. Jobs could be immensely tedious and fatiguing, a world away from the concerts, games and other recreational pursuits working men imagined were avaialble to 'Stalag Wallahs'".

So there certainly were prisoners who did their best to carry on the fight in some capacity with various motives from patriotism to boredom, and post-war accounts have focused on them, but for every case of a potential escaper eagerly awaiting [a Monopoly set containing a map] (https://www.reddit.com/r/AskHistorians/comments/7a5dof/is_it_true_that_the_allies_sent_pows_monopoly/dp7qrrw/) there were probably several others who were more interested in the game itself to break up the monotony.