why would a game console need a sleep tracker though?

Not necessarily. Stocks sell on speculation, rather than results - unless those results lead to higher expectations. This typically isn't the case, as market analysts are usually fairly close. Pokemon is very predictable given the long history of the franchise, they have done the market tests numerous times. They analyze the market health of consumers (that is, a measure of how much they are expected to purchase in the future based on the schedule, and how much longer they're expected to continue being a Nintendo consumer). This is why you see some (what appears to be) wacky behaviour on the stock market, where a company reports phenomenal quarterly sales, and then the stock value drops; or even stock rises after poor sales results. It's based on speculation of the future, rather than sales results.

It's a product that is expected to drive hardware sales. Especially considering Nintendo's consumer base is largely families where fathers and mothers are consumers, and sleep is especially important - this makes for a good sales pitch; the shareholders voted positively on it.

Why would any console need a scale though? Nintendo showed with Wii Fit that QoL could be a huge market for consoles. There's no doubt that investors were anticipating this project to attract people who might not have gotten a console otherwise after they heard that it might be able to help them sleep better.

That said, I think this is more just a market correction after people sold their stocks after the hype of Pokemon Switch announcements.

I though I remembered hearing the the QoL concept was scrapped before they even formally announced the Switch...

https://kotaku.com/nintendo-investor-i-do-not-understand-video-games-1599625657

I know how the markets work I work in a financial institute, if the stock tumbles today then no doubt it's at a lower price then when Pokemon arrives later on, buying the stock now and going long on the stock will net you profit when the game arrives and with two Pokemon games you can exit the stock when it reaches the high of the first then enter when it drops again to go long for when the second game arrives, Pokemon will be the biggest boost Nintendo will have over the next year.

It was a backup strategy in case the Switch also fails. Makes sense to scrap it for later.

Right, this was hardly anything to get the market upset but hell, I'm taking the opportunity. 

We have been hearing QoL as third pillar for what feels over 5 years. I thought it was already dropped.