Implying I care about making music? It's a different hobby all together. They merge to some extent, but I enjoy designing synths much more than I do making music on them.

I enjoy the act of building. A person interested in writing software doesn't have to care about using the software. A person interested in fixing and building kit cars doesn't have to care about driving them. A person working out can be doing it because they enjoy it, not because they care about any end goal. A person baking bread doesn't always have to eat it. A person painting a picture doesn't have to adorn it on the wall when they're done.

There's a lot more to hobbies then just what you get at the finish line. The process is often much more fun than the result at the end of it, or what you can do with that end product.