Shovel Knight was Kickstarter, IIRC, which amounted for basically all of that. And I'm not saying the game had a lot of money poured into marketing, but these games rarely get a trailer shown as more than a part of a montage at E3, let alone time at multiple conferences.
This is ultimately less of a D4 thing and more that Microsoft has been poor about advertising digital-only games on Xbox for a long time. For Microsoft, this got a lot. But people not tuned into Xbox media channels (like the trailer they put up on their YouTube channel or the featured spot it got on the dashboard) would easily miss it.