I'm sure someone else said this before and I'm certain that they said it more eloquently than I will.
Tabletop RPGs aren't just a single hobby. They are an axle around which the spokes of many hobbies revolve. They are the gateway that allows participation in many different (related) hobbies.
For example, I'm a writer because of D&D. I wrote this little book, I'm working on another (slowly) and I'm rolling other ideas around in my head for a third.
I write adventures too. I write spreadsheets and other software tools to help me run games. I write this blog.
What's more, I'm kind of a hack artist too. I like to draw maps, monsters, magic items, etc. Sometimes I use pencil and other times I use GIMP. It's fun.
I'm also a minis painter. I do crafts. I invent all kinds of things.
I've even built a rolling DM station that stores all my minis, includes an LCD projector, is my DM screen, contains frequently used charts... (I'll post about this very soon)
The bottom line is, what other hobby lets you do all these other hobbies too? Hell, it practically compels you to do these other hobbies too...
...and I haven't even mentioned ACTUALLY PLAYING THE GAME as a hobby in its own right. :)