I'm ashamed that I was completely guilty of this myself.
At some degree of professional development in software, you start to verbalize things, so as to 'explain them to yourself' and it helps clear things up.
This helped me understand that 'writing skills' (in this context) are frankly more matter of being able to organize concepts more than anything else.
A dev who can articulate is literally worth at least 50% more than one who cannot.
And to your point, yes, it's funny and scary when someone can't describe something they ought to be able to.
If someone can't explain something they are actually a risk to the code.