Aerobatic flying is risky, even more so at night where the references of your safety envelope, like the ground, aren't as apparent. The ace in the hole for aerobatics is horsepower, to be able to correct for miscalculations and surprises.
With a glider, no power to get you out of trouble, a sudden change in turbulence or gaggle of geese could spell disaster. Also, the additional strain on the airframe from the weight of his balls.
