I think it's largely about the marketing aspect. Imagine creating marketing for Crusader Kings 2, Mount and Blade, Terraria, and the countless other games which sold a zillion copies and are unbelievably fun, but just look pretty bland on the surface. With high end voice acting, lots of cut scenes, and so on - all of the marketing basically writes itself.

You have your actory voice intro the game, set the stage of the plot, show some brief segments of critical moments in cut scenes, and then occasionally intersperse a half second or so of actual gameplay. No idea why this gets some people fired up, but it seems to work reliably enough. I suppose it's just targeting a demographic that isn't you nor I!