I joined because it offered server access similar to what I received at University and I've moved a bit and this allows me to keep my internet presence stable. It's a great set-up and community. These days it is less necessary due to the rise of cloud based VPS providers, but it offers more of a community compared to those. the other thing is commercial operators come and go. SDF has been around for a long time and because it is community driven it is likely to stay. The fact that it has been around longer than any other alternative also attracted me to it.