Why doesn't my best friend ever want to hang out?

Hello! I'm a woman in my mid-thirties and I met "John," a man in his mid-twenties, through work. We developed a strong connection over several months, and he eventually told me I’m his best friend. We communicate every day, whether through work or texting. I've tried inviting John to hang out—nothing too intense, considering he deals with anxiety—but he always declines. In fact, over the past year, he’s never come to my house, and I’ve only visited his once just to drop something off. I don’t understand why. The only times we've been able to meet up outside of work are when we attend mutual friends' gatherings, but even then, he frequently opts out. John has some quirks and personal struggles, much like I do. I don’t expect him to be available all the time, but it feels odd to think that a best friend wouldn’t want to hang out at all. I’ve directly mentioned that his behavior seems unusual, but he just brushes it off with a nonchalant "I know." He claims to value our friendship and is genuinely a kind person. So, what’s going on with him? How should I move forward? I can’t help but worry about what will happen when we can’t stay in touch through work and will only be able to communicate via text. Does anyone else experience this? Edit: I also want to mention that he often expresses feelings of loneliness, which adds to my confusion. It’s one thing to be less social, but it doesn't make sense to complain about loneliness while avoiding in-person meetings. It puzzles me how someone can be comfortable being best friends but rely solely on digital communication—something that could change in the future due to work shifts. Maybe we just have different definitions of what being a "best friend" entails.