Multi-platform games have got a lot better about PC-specific feature support in recent years. These are not the dark days of 2005 any longer.
That said, things like multi-monitor support and dual-GPU optimization is a very niche feature on PC. I'd be surprised if dual-GPU accounted for more than a couple percent of players, for instance. Supporting those features usually doesn't lead to any more sales, and usually takes more than that percentage of work than most think - if the tech being used can even support those features well at all. Between putting engineers on features everyone can enjoy, vs. just a tiny sliver of users, well, it's not surprising why certain choices are made.
You actually tend to see a lot of niche feature support in other genres though, like simulators and MMOs - usually because those games are supported over longer periods of time by a dedicated community, so the developers have more incentive (and time/money) to appeal to those guys.