(I use this in workshops.)
1. You get to control the world. Well, the world of your story, that is, and the people who live in it. You are the goddess, the supreme puppet master. You even make the weather. How cool is that?
2. There's no right way to do it. There are suggestions, and lots of people will tell you about "rules" and "musts" and "shoulds," but for every such rule, there are plenty of successful writers who break it. You're freeeeee!
3. There's no expensive education required. In fact, I think the best way to learn to be a writer is to read, and all you need for that is a library card and access to a library. Yes, classes and workshops and conferences are good, but it's not like a writer has to be board-certified or anything.
4. There's no expensive equipment required. Well, okay, a computer is, I think, necessary in this day and age, and internet access, too, but when you think of what it costs to set yourself up in many another business? Not a lot of overhead. In fact, you can get started with a pad of paper and a pencil from the Dollar Store.
5. No meetings! No sitting at a table in a little room listening to somebody drone on about something while all you can think about is the work waiting for you back at your desk.
6. You can do it in your jammies. (I don't, but I could.) That also means you don't have to go outside in inclement weather.
7. When you sell, it's all yours, baby. You did it -- not a group, not a committee, you. You had the idea. You wrote the book. Your critique group and/or agent may have helped, but it's mainly because of your hard work.