Give him a break, he needs to milk the cow :)
Let's be honest: before Inglorious Basterds, hardly anyone knew Christoph Waltz. Even in Germany, where I live, he wasn't particularly famous (and German movies are known to cast Austrian actors just as keenly as American movies cast Canadians or British). He had 30 years of a small career on the shadows: small films, TV, theatre.
He was 53 when his big break came, and if you had an opportunity to suddenly get cast in big productions at 53, you'd seize it any moment. There are hundreds of actors in his age who used to be famous and would now kill to get cast in a Bond, PotC or some comic-book screen adaptation, because it pays.
A lot of great actors take these jobs: Ian McKellen, Patrick Stewart, Jeremy Irons. They star in a few big-budget movie productions, cash in a few millions just to have a solid retirement fund.
Christoph is 58 now, he's still fit and in great shape, but who knows how long it'll last? So he's seizing the day.
Plus, as weird it may sound, even those unambitious big budget productions are an interesting challenge for an intelligent actor. Maybe the acting material isn't great, but you get the opportunity to work on a high-production-value film: elaborate sets and costumes, green-screen, motion capture, CGI. Being part of such productions is a hell of an experience for a mature actor such as Christoph. He can learn a lot, should he, for example, want to take a shot at directing. I'm sure Christoph would also love to take a part in some Planet of the Apes film so he can do motion capture acting loke Andy Serkis.
Christoph Waltz has achieved a lot: two Oscars within a few years after decades of being a virtual nobody -- many other actors must be incredibly jealous.
Even if he ends up being typecast in his age nown in Hollywood -- who cares, he can still use the money. As long as he gets to play the occasional villain in Hollywood, he can always do more ambitious stuff in European cinema or in theatre. That's what Irons, McKellen, Stewart etc. do.
Plus, Christoph's choice of Hollywood parts hasn't been that bad either. He had a lead in The Zero Theorem, a Terry Gilliam movie! You don't get lead roles at the age of 55 or 58 often.
Well, unless you're Liam Neeson, whose career is even more impressive. Who'd think he'd be able to become an action movie star at 60, while previously playing mostly romantic or "well-behaving" parts?
Look at all the other great actors: Dustin Hoffman, Jack Nicholson, Robert De Niro, Michael Douglas -- all they do at their older age is American romantic comedies. I bet they'd trade with Christoph Waltz any moment :)