While it would be great to see an uptick in quality branded games, there are definitely some barriers. For one, the skill set for making fun, simple, casual games isn't especially widespread -- it seems like it's easy to make an OK advergame, but very difficult to make a good one.
That said, with all the tools available on the wide variety of social media and content sites, there are many ways that companies without a lot of experience in gaming can nonetheless create a strong casual game offering without necessarily outsourcing or hiring someone with the video game developer skill set. A great example is a a simple choose-your-own adventure game developed by the English Metropolitan Police, designed to educate British youths about the dangers and consequences of carrying knives (and the fact that British police can search you without probable cause, apparently). The game, while very slickly produced, only requires a solid understanding of YouTube annotation functionality and video production skills -- something any medium-to-large-sized firm should be able to muster.
An advergame doesn't necessarily have to be developed from the ground up. The existing tools that exist in the social media space provide a great playground to work with -- with the extra benefit of being spaces where users implicitly understand the rules and mechanics by which you can play. For brands looking to get their feet wet in the world of gaming, they might be a great place to start.