I would probably just boil it down to an appreciation of finely-machined things - like a nice mechanical watch. I like seeing interesting and purpose-built tools that are both enjoyable to operate (really, play with) and there's the added bonus of having a cutting tool on me whenever the need arises.
That said, I don't typically even bother to explain the knife hobby to anyone, though - the topic just doesn't come up. The most conversation I'm likely to have with a non-knife-bro is something like "thanks" after they say "nice knife" if someone happens to see me using one, or "It's fun / well-made" if they ask me why I need a knife that large and/or conspicuously expensive.
Like any hobby, it really does take a personal interest for it to make sense. I 100% don't understand the draw of, for example, Warhammer 40K. The gameplay and the craftier hobby aspects of it just seem incredibly tedious - but I'm sure there's a whole set of forums of people spending hundreds of dollars, taking pictures of their painted figures, recalling cool moments, etc.