No, it's not because they have a tailwheel. It's because by the time you've managed to learn to control their cantankerous behavior, a previously elevated portion of your anatomy is bound to be dragging on the tarmac as you skulk away after your first crosswind landing. For proof, read Glenn Daly's riotous account of his experiences learning to tame a wild Citabria. The author in a moment of self-assessment following his first taildragger lesson in the Citabria. W e tricycle-gear drivers don't know jack about flying.
Tricycle gear makes nearly every landing a greaser.
Try flying a taildragger. And, while I admire his accurate and entertaining appraisal of learning to fly them, I think he quibbles about his definition. I call them taildraggers because, after the first few attempts at flying one of the squirrelly things, it was my tail that was dragging. Oy, whatta pain. Then, when drag your sweaty carcass out of its cockpit, you stagger around like a drunk on a three-week bender, your feet moving independently of each other.