To be completely honest, I think is was made primarily with the intent to allow for pirating copyrighted NDS games. I don't think there's really that much money in homebrew. It would just be a very bad idea for the manufacturer to admit that. Last I heard, Nintendo were trying to shut them down anyway.
Oh, and I too find it easy to use. I'd go as far as saying very easy. You basically just drag-and-drop the software onto the micro DS and it works right away (with a few exceptions).
There's no way Nintendo can shut these down, it's legally not just not possible. Also they aren't illegal anywhere yet I heard. But i am willing to bet the prime reason for these are to help pirate NDS games. Of course there's some problems with doing that.
1.Your making steal games for the DS really easy.
2. That then drives down sales.
3. companys produce less and less games for the DS due to decrease in sales.
4. nintendo stops making nintendo DS units since no one is buying games for it anymore and few companies will make games for it.
This whole thing is why I still buy stuff I like to avoid a situation like this. I hope all video game pirates do the same, but I know some of them don't. We might not have to worry about a company like Sqaure Enix going down but a company like the one that made Indigo Prophecy and Hard Rain (coming to PS3) is rather small. Plus they don't have a bit fanbase yet, though they do have a small devoted one.