I think people who are into crafts. They have all of these yarns, construction papers, various tools and stuff. All so that they can say that they have all of these projects in mind that they want to do. But they never do them so they get more crafting stuff and it just eats away storage until their place is practically consumed by it.
But you need equipment to actually play?
I’m not a guitar collector/fetishist at all, but still need at minimum an electric (preferably at least two for humbuckers & singlecoils), a steel string, a nylon string and a bass to be able to play what I want to play. Not to mention amps, pedals etc. And this is strictly for playing gigs and home practice, when you get into home recording it piles up even more. Even if you restrict yourself to things you actually use, the possibilities for hoarding are pretty much endless.
Yeah collecting instruments, parts, strings/reeds, and accessories is totally part of it. People hoard to varying degrees but any hobby requiring physical objects is hoardable.