Antiskid
$20 cost for 10 mins as compared $100 plus for larger aircraft. Seems to speak for itself. ATC try to reduce costs for everybody, but have to prioritise. Seems the training aircraft are at the bottom of the food chain.
You will be logging the time on the ground anyway. "Chock to chock" they say. I understand you would rather be in the air. But everyone has gone through it at some stage