So if he doesn't love to teach, he doesn't love his art? I'm really trying to wrap my head around what you're saying here.
People love what they do for different reasons.
I trained "traditional" Japanese karate for almost 7 years, took time off because life got in the way, then resumed almost 17 years later. I've been back 2.5 years now. I taught during my first stint because I liked teaching. I wasn't forced into it, and my sensei was allowing me to train for very cheap. Teaching wasn't on my radar, but my sensei thought another classmate and I had the personality, knowledge, and ability to become very good teachers. I tried it, and I started enjoying it, so I taught more often. We weren't asked to teach because he wanted to hang out and do other things. There were higher ranked and ability students who were never approached to teach.
I'm now going on 41 and am a school teacher. Being in another "traditional" Japanese karate organization, I have next to no desire to teach. I like helping out classmates before and after class, and I enjoyed helping teach my daughter's class when she was there. I wouldn't mind teaching a class or two if my CI asked me to when he's away. But regularly teaching? Zero desire to. And I LOVE karate. It dominates my thoughts when I'm not at work or hanging out with my family when I'm not in the dojo. I'd like to think my knowledge of it combined with my physical education teaching experience would make me a very effective karate teacher. But I'm at a point in my life where I want to train and learn karate.
Not wanting to teach doesn't make me a bad person, karateka, nor anything else. It's just not my thing. It has absolutely nothing to do with a lack of love for the art. Not everyone fits the same mold. Thinking they should is absurd. Thinking if someone doesn't want to teach will mean they won't stick around long or they should take a different art is even more absurd. There's several people at my dojo who've been around for 2-3 decades who have no desire to teach class. They like helping and working students individually, but they have zero desire to run class. And I'm pretty sure they wouldn't be very effective in that role. They'd be quite effective in a tutoring role, if you will, but they don't have the personality to regularly run a class. Even the smartest and most effective people in any field can't teach. That's just the way it works.