It’s not really so much that there’s something wrong with him, it’s just that you’re probably used to just having conversations with people that you’ve been having conversations with for years and years or that you already have a lot in common with.
If you really want to invest the time to work on this aspect of your relationship then this is how I’d go about it.
Find something he thinks is interesting. Ask him a question about it. Let him ramble on about it. Try to listen to the thread of the things he’s telling you. If anything he says to you confuses you, ask him a question about it.
Right now, you’re just trying to get him invested in conversation, so you’re making it really easy for him by picking a topic that works for him and priming it with questions, and keeping it going all by yourself.
Do this a few times and he’ll start thinking you’re actually interested in that topic. Which, if you have been truly paying attention, you just might be. Go out onto the Internet and read more about it. But since it’s his baby, he’s going to start conversations with you about it. Sit there and listen to him.
Eventually you’ll always be able to have a conversation with him about that topic because you’ve invested enough into it to make it worthwhile. What you have to do now is branch out to other topics. Stay in the realm of his general interests, but branch out a little further every once in awhile to something you like, like throwing out a lure, and see if he bites. Eventually he will.