I was interested in reading online manga. That was the beginning. Then I once worked on a manga scan group which is now dead. I enjoyed working there, and added with my random curiosity, I decided to try building my own manga scan group.
It's all started because of my hobby, I guess.
I enjoy cleaning and typesetting, and later on, I found out that I've got a bunch of Manga raws which seemed to be nice enough to be scanlated. I mean, why not?
Not to mention that I can't translate Japanese/Chinese, so I guess it's better to make a Scanlation, then work out for those Raws. If you know what I mean. It's just about hobby for me...
I find it very entertaining and a fun hobby to pass time. It is a nice reprieve from the stress of daily life and the other things I have to deal with. The community within itself is fun and very pleasant.
Typesetting/Redrawing/Cleaning is pretty fun and can be quite relaxing, since it's pretty stress free unless you're working under a deadline.
Translating is a different monster and accounts for most of my stress when it comes to scanlating. However, it's a pretty good way to keep up with and practice reading Japanese. I scanlate because I want to and when I want to, so my reasons are mostly selfish. But it's also a good way to give back to the community what it has been giving me for a decade, especially since I have the occasional time and energy.