I think a lot of gliders pilots wouldn't mind having a transponder if they could have one, but the kind they need are just now getting available and still too expensive. For one it's a weight problem, then the matter of where to put it... there isn't much room left on the panel.... then there's the problem of the electrical connection.... the normal glider battery would just die out too soon. If these problems were already solved, then I'm sure they would already be required! So, let's just wait until the proper equipment gets available.
As to balloons... they, too, they are not required yet. Here there is also the electrical problem... without a motor, no electricity!!
I always say, if everyone would abide by the rules (restrictions) already in effect, then we wouldn't need new ones! But when you hear about some idiot glider flyer circling above Frankfurt airport within airspace "C" (he was seen by an Airbus... of course ATC couldn't see him), then no wonder we get more and more restrictions!!
Westy