Garrulousness is the habit or quality of talking too much — the thing a garrulous person has, not the person themselves. Writers use it when they want to name the overflow as a trait: a meeting runs late because of someone’s garrulousness; a long journey is worn thin by it. It is a formal, slightly heavy noun; in ordinary talk people are more likely to say they talk too much, they never stop, or they go on and on. The judgement is the same: this is quantity that tires people, not lively conversation as a gift.