I think this is two fold too. This works in his advantage and solves two issues.
1. He gets to be involved with and help another company build this and get some profits off it. He gets to hype it, and help with the initial stuff it sounds like. Win win for them, for Elon, and us humans.
2. This thing is going to be lined with solar panels, he even said it can generate more power than it needs and will have an excess of power that needs to be dumped somewhere. Hmmmm, who owns Solar City... who owns an electric car company that is dying for recharging stations on the West Coast... Think about this. He gets the government land to have whoever/him build this, and throws a couple charging stations along the route to boot, and it's all conveniently located on an interstate. He gets charging infrastructure which helps his other business Tesla. Everywhere they build one of these loops, right along the freeway, could also come some charging stations. He eluded to this in another interview that I can't currently find.
This is more than just the Hyperloop, this is infrastructure that pairs well with his other projects. The man is a genius.