My response was to your second point where I assert that some people derive pleasure from things that others perceive as mundane. Eating at a 4-star Michelin restaurant for example can be loosely (very) compared to writing with a $60 pen. So it's not bizarre.
To your first point, deriving pleasure from doing something does indeed encourage you to do more of it. Even eating - compare eating a mediocre meal at a food court to a scrumptious meal prepared by your mother (or whoever cooks well in your family!). Sure, writing is not an infrequent exercise, so perhaps the analogy goes only so far, but the point remains that if you enjoy it, you are likely to do more of it.