Some people are like that, they don't talk too much, that doesn't mean they are bad people or bad partners. But I understand for other people, especially their partner, it can be a cause of concern. Well, there isn't much that you can do to make them speak more, but you can tell them that this is bothering you. Your partner might try to talk to you more. Another thing that you can do is take more interest in their passions and hobbies, that can be a good way to strike more conversations with your partner.