I raised a cribber. She’s now 20.
Mom did not crib. Dad did not crib. However, I 100% believe it is a genetic predisposition.
She was 3ish when she started cribbing out of the blue. She lived an idyllic life-- full-time turnout in a 10+ acre field with a lovely herd that included a same-age playmate, two older mares who kindly enforced manners with the youngsters, and the world’s greatest gelding-who-thought-he-was-a-mustang-stallion, who kept the herd perfectly in line with no more than a glance. She ate nothing but good pasture, good hay, and a ration balancer. I don’t think she knew what stress was.
With all that said, this horse’s brain is definitely not wired typically. 
At one point, this mare’s BFF was a very stressy, anxious horse who tried to copy everything my cribber did, including cribbing. But it was hilarious-- she would place her teeth on an object, just like her friend was doing, but clearly could not get the action down or understand the appeal. Eventually she stopped trying to copy. To me, that definitely busts the copycat myth and indicates there needs to be an underlying neurological or genetic predisposition to pick up the vice.