I'm in this more for the open-sourceness of it.
As a big open-source advocate, I like supporting things that upset the established order, especially big companies like Facebook and Tumblr, that take advantage of their users.
I'd much rather give my support and effort (and even money) to an open collaboration, rather than let those fat cats get fatter.
What it comes down to is I have a few interests that I'd like to write about. I'm not sure that anyone else will really care what I write, and sure, I could start my own blog, and have tried that a few times, but it's about as much effect as screaming into an oncoming storm.
At least here someone will look at what you write and if it's useful, maybe some more people will look at it. If not well, it's my fault for writing useless drivel, not just whatever I write getting lost in the internet, you know what I mean?
Yes, that's a great attitude to have about it. Many of us here are of the same opinion, so you'll fit right in and do really well. :)