If you were in the RAF you would wear one because they do. In the civil world they don't because thats what they do. Give civil pilots them the option to jump out??? you'd have the country littered with aeroplanes without pilots, encourages LMF etc etc.
You jump out of a plane if its on fire or the wing breaks, in all other cases landing is safer they say. Gliders fly right next to each other in thermals so higher risk of collision.
If the wing came off the aircraft it would be moving about spectacularly, a 100 mph wind would be the least of your worries.
I think we stopped wearing parachutes when they tried to make aeroplanes like cars, out with the 5 point harness, in with the 3 point inertia reel and comfy seats. Wearing a parachute means you will crash, scary (and it creases your suit)