I don't know why so many people reflexively go with this option. Activision is a ridiculously successful company, and I have a very difficult time imagining their management is made out of morons with an eagerness to lose money. $500 million is a fairly manageable sum for Activision, and that investment is going toward building a franchise that most definitely has the potential to generate billions of dollars over time. I'm pretty sure a robust monetization scheme was conceived long ago, with a variety of revenue projections for the next decade nice and calculated. It's certainly a big gamble, but I'd say the risk:reward ratio in this case probably makes it a sensible one.
I also don't really understand all the "this is what's wrong with the industry" doomsaying. Is GTA V also an example of what's wrong with the industry? I mean, yeah, the AAA business model generally has issues, no doubt. The market has changed, technology has changed, developers have a challenging environment to navigate. A blockbuster budget isn't inherently a bad thing in and of itself, though. In this case, Activision is competing with the rest of the industry by doing something it's uniquely capable of: taking in a lot of risk, and creating something of a massive scale. It wouldn't be the first such project to fail dramatically, but it also wouldn't be the first to succeed.