You sound just like me. I find a new hobby, learn all about it, get good at at, then I usually end up losing interest. It is very frustrating. I’ve been through so many hobbies and interests it’s kind of ridiculous. My mom jokes that I’m a skill collector. I think that’s kind of a nice way of looking at it. I know it doesn’t help with the frustration, but I feel like it’s a more positive perspective. Just think about all the neat skills you’ve learned from your hobbies. Eventually you’ll probably find something you want to stick with. My latest hobby seems to be sticking (aromatherapy), and it’s been over 2 years. I’m actually taking a certification course, and planning on turning this hobby into a business.
As for hobbies you don’t feel at all interested in anymore, see what you can get for your supplies on eBay (or Facebook groups). Then you’ve got some extra money to put towards the new hobby.