I've had a few that ran short. Some of them its obvious they've found someone already (or had a particular person in mind and are going through the motions.
Others, especially i think the competency based ones, I think I've sometimes answered 2 questions at once from their set, so it shortens it - e.g. tell me about a time you dealt with an angry customer (with their next being something like tell me how you went above and beyond) - and my example covers both.
I mean I can also talk at the speed of light when nervous, so I probably put out a lot of information in a short time...then get worried it went quick. If that's you too, making a conscious effort to pause, breathe and slow down might extend a fast interview to a normal length one!
Do you ask for feedback if you don't get a role? Aside from the super unhelpful 'you were great but the other person was more experienced', sometimes it can help you work out if you're consistently missing something.
Ultimately if you're answering the questions with a fully formed answer rather than one word or one sentence then its not too much of an issue. I think if your experiences are different to the employer, you have to spend a little time on explanations, whereas if you have a lot of common knowledge or simple situations, its easier to forgo the context and take less time, just with only the job-winning details.