I've rather suspected it was a combination of shyness and fear of not getting it right. Still, I wish they'd learn that the rest of us are very forgiving or mistakes and that use would improve they language skills. *sigh*

As a teacher, I feel that way too. Sometimes I feel kind of guilty, because I rarely talk during my daily life either, concentrating mainly on reading. However, I do think taking a language class that includes communication as a goal puts one in the position of being obligated to practice speaking the language. It's a different context.