FEAR...fear would be a good word why people tend to stick to the more commonly worked terriers,patterdale,lakeland,fell,russel.
Fear of putting all that time and effort into a dog and even getting a decent bond with it...just for it to fail.There is a risk with all terriers or working dogs for that matter,however well bred however game the parents are ,that the pup just doesnt make the grade.
It is a great gamble to invest all that time effort and even money into a well know proven type of terrier without even taking greater risks with types that could almost be described as one offs.
I wis