Okay, this is probably crazy as hell, but hear me out a minute.
Basically, Nintendo doesn't seem to be advertising WarioWare Gold much, especially outside of Japan. This means it's unlikely the game will sell too well in most parts of the world, since no one really knows it exists outside of the hardcore fanbase.
And that made me think. What if... we literally marketed the game ourselves? Could we really just buy ads for it on sites on Facebook/Twitter/whatever and send all the traffic to Nintendo's shop page or what not? In theory it seems possible, and may bring more attention to the game.
An intrepid idea, but I doubt a few sidebar ads would have much of an impact on the game's sales figures. Let's be realistic; this is WarioWare, one of the most niche core franchises of Nintendo's modern repertoire. By virtue of that fact, Gold's audience is already decidedly small, but take into account its status as a filler/c-list title to squeeze a few more drops out of the sinking 3DS, and it quickly becomes apparent that Gold was doomed to the "quick buck" treatment from the beginning. It may not be quite as uninspired or cheap as some of the other 3DS filler slated for release (such as, oh, I don't know, the endless stream of pointless downgrades remakes), but it's nonetheless obvious what this game's duty was: make a quick, simple buck off of stubborn 3DS owners and shut up the Wario/Ashley/who-the-Hell-ever fanboys.
Nintendo knows that most of Gold's potential audience on the Switch is wasted on the 3DS, and that's why it's a cheaper title rather than a full-blown, big-budget, brand-new installment in the Ware series. This game's audience is comprised strictly of those who can't afford a Switch, and perhaps a handful of Wario fans. There's probably not much one could do to sway the vast majority of Nintendo fans who've long since nestled into the Switch platform.
