This is probably more a problem of expectations in pair programming than pair programming. It comes the easiest to extroverted people with "standard" thinking patterns that are mappet to language 1:1, I also have to translate thoughts into words which is more of an effort than actual coding. But you don't have to express everything with words, if I can see what you are doing I can just follow that. I can't imagine doing it always, but for onboarding and from time to time its great. Not just for knowledge of the system, but learning how other people flows are completely different, what tools they are using and how their workflow looks like, etc.