Why might you run your own DNS server?

One of the things that makes DNS difficult to understand is that it’s decentralized. There are thousands (maybe hundreds of thousands? I don’t know!) of authoritative nameservers, and at least 10 million resolvers. And they’re running lots of different software! All these different servers running software means that there’s a lot of inconsistency in how DNS works, which can cause all kinds of frustrating problems. But instead of talking about the problems, I’m interested in figuring out – why i...