The bottom line is there are hundres of wannabe tug pilots queueing up at gliding clubs to fly the tug. Who wouldn't want to get dozens of hours and hundreds of rotations in for free, especially at a gliding club which isn't tied up with procedures and ATC etc. So most clubs already have experienced glider pilots and power pilots from within their ranks and from other gliding clubs in the country queueing up at the door. Even if you are one of the lucky ones and you get your name on the tug pilot roster you can usually only expect to get a few days a month. If you can't fly midweek that drops to half a day once a month.
So it's not necessarily that flying the tug is difficult, or that power pilots can't learn to be good tug pilots, or that gliding clubs have a clique but that if you have little or no gliding experience there is always going to be someone else who is better than you.