Because the people who tend to care the most about stuff like what Reddit is doing or about having a long-term community moved here; whereas the people who just wanted a quick and easy way to learn how to download warez stayed behind.

I don't even mean that in a critical way (a lot of us started out like them, and there's a limit to the number of things people can care about anyway) but that's more-or-less what it is. The people who came here are the ones who care more about piracy in-and-of itself and who often have ideological or philosophical reasons to support it; and they tend to be the ones who make the most interesting posts.