Because in a non-lucid dream you don't have to deal with conscious thought. Not surprisingly, conscious thought takes focus away from the dream environment, and if you lose sight of what's happening around you, well. . . you really will lose sight of it. This probably makes you think you're waking up, and, building from that, your dream runs with the idea and "restarts" with you back in your bed.

May I ask, what methods of stabilization have you used in the past, and how would you rate their effectiveness?