There are very few things I've used more, maybe my mattress? Office chair? My shoes? Not my car, not my bike, none of my 'real hobbies' that I get to enjoy for an hour a day or maybe two on a weekend. And I don't want to get too real, but I've probably touched my keyboards more than I've touched my wife, and now I'm sad.
There are certainly "collectors" who get a kick out of just spending money to line shelves with a variety of objects on display. I also don't understand that. But keyboard hobbyists are typically also typists, who use their keyboards, and try new styles frequently to find the best tool for the job they spend most of their lives doing.
Clearly you've never built a keyboard or shot a gun, there is plenty of physical and mental challenge if you want there to be. I've never gotten into knives but there's absolutely a huge physicality aspect if you go down the self defense rabbit hole there - huge in certain martial arts. But regardless, not everything needs to be a challenge and not everything needs to have "cultural or aesthetic enrichment" (although I'd absolutely disagree on your assertion there's no aesthetic component to keyboards or firearms).
Feeling the need to diminish what other people find joy in is the hallmark of a sad person.
I majorly disagree, despite not having a mechanical keyboard. Some keyboards are absolutely beautiful. You get folks putting stones and miniature figures and what not on their keycaps. If you don't consider that art, I wish I could show you how others do.