It's elitism and it's a bad heuristic. There are lots of situations where someone might know a lot about X yet for some reason never did X. Being able to do X,

It's elitism and it's a bad heuristic. There are lots of situations where someone might know a lot about X yet for some reason never did X. Being able to do X, and being able to usefully explain X are two different skills and few people can do both.