That's quite an assumption. You've never heard of pair programming? You've never asked for help on a bug in your code? You've never talked through alternate approaches to a piece of code with a coworker? You've never hashed out an interface or a method signature or some pseudocode while talking through the problem? You've never walked through a calculation with an SME? All of these are "code and talk at the same time" exercises.
If I'm being brutally honest, I have a deep-seated suspicion that everyone who says they can't talk and code at the same time also just cannot code at all. I don't know you, of course, and I'd love to be proven wrong. My sample size is small, but the few people I've met who cannot talk-and-code also simply could not code.
