There are a couple possible reasons why....if it was run hard on a weak top end for a while, that could have done it, old age of the rings- it was just it's time lol, or lack of lubrication.
Usually the first one is the reason why MORE damage occurs to 2 strokes when they fail. I know from experience that when mine was low on compression I could have saved a cylinder by NOT continuing to try and run the crap out of it.