However there have been many cases of when people have bailed out, due to control issues and other factors. For example a JS1 when the rudder pedals moved away from the shorter pilot, became unreachable and unable to be adjusted, forcing the glider to lose control. Pilot bailed out and survived. Likewise there are examples of a mis-rigged glider going up a winch launch without an elevator connected, and by sheer luck reaching the top. The pilot(s) have then bailed out from at least 1000ft QFE and survived.
I've only flown gliders twice, and really enjoyed it (they're less common in Canada). From the passage above, I could get the impression that there is less vigilance about assuring the aircraft is flight ready before beginning.
I have had several aircraft which were very difficult to fly due to control failure and misrigging following errant maintenance, which as the maintenance check pilot, I was first to find. These hidden defects were very difficult to detect in a pre flight inspection (though I'm learning to be more invasive in my walkarounds!). But I still would rather have fought the aircraft back to the ground, than consider getting out of it!
But, I do see the difference in being towed up hundreds of feet, to then find a problem you can't handle. I accept that gliding may be more risky.
In the genre of flying I do, I have never heard of an after the event discussion which went like "wow, if that pilot had a parachute, and got out, he'd be alive today!". I suppose there have been some, but I've never heard one. To a larger extent, fatal accidents are either CFIT, or otherwise so low that exit would not allow successful parachute deployment, or loss of control at altitude so severe that exit would not have worked (spiral dive).
In the military, parachuting, experimental flight test, aerobatics, and 'sounds like gliding, things are different, and parachutes may be appropriate. In my opinion, not GA, when flown with the intended diligence.