There's no need for a standard API when it's all software, that's the (great) point! Games aren't licensing middleware or doing it themselves simply because the vast majority figure it's not worth it to their end users. This is a communications/user problem not a technical one. People simply need to emphasize their desire for better sound to developers more. There are zero technical barriers in the way here.
I have a sneaking suspicion this has to do with companies either erroneously or indifferently labeling audio as "post-production". So like if you were a graphics artist and you showed up to work on a game and the programmers said, "alright, we're done, just stick the textures in this dir and the models and animations in this one, and burn a cd when you're done," you would probably be a little concerned. But this is probably about the level of "sound design" most games receive, judging from the product. For example, I can load up numerous AAA shooters from the last year or two where bullet impacts sound the same irrespective of what they're colliding with.
I figure the current state of affairs is probably due to the industry's unhealthy obsession with graphics, but also the unhealthy and deranged obsession with emulating movie/TV productions.
OT: Anyone else getting pretty excited about this here game? I am.