Because it is inherently attractive to people who have worked client side in javascript and want to expand. Like me. I'm relatively new to the industry. I know javascript fairly well and while I might not be as familiar with the sort of problems that have to be solved on the server I am learning.
I think a lot of the criticism about people getting into it thinking that they can just port their client side experience to the server is valid. But the tone of so many seemingly anti-node posts turns a lot people off. I read more critical posts about node than I do positive ones because I know I will learn more. But sometimes it is not easy to cut through all the ego thumping and noob bashing. It would be nice to see the tone of the discussion shift, which I think it is starting to do, to what node is actually good at (in my opinion it seems to be acting as a glue for applications that require real-time).
Regardless, it works. I've started using Trello and I love it. Best organizational app I have used. Built in node. It works and I have not had a single problem with after two weeks of pretty heavy use.
So I don't think it just won the hype lottery, it has distinct advantages over Twisted and EventMachine, even if many of those advantages just have to do with relative accessibility and the ease of access provided by NPM.
It has hype because it has an involved and open community. Not just because it was lucky.