How is it not?

We're talking about a major source for Nintendo's revenue here though. Their console. And about major investor. They don't buy that much without getting filled in on what their money is going towards. They didn't get rich by making uninformed decisions.
So if an investor wants to sell because Nintendo doesn't want to share their plans, then a potential buyer would have the same issue. Nintendo can't keep shareholders if they withold this kind of information from them. Imagine not knowing that you invested millions in the WiiU.
Nintendo can trust their investors with their information because it's their money on the line.

And sure, there may have been leaked info from an investor at some point or other. And that info gets treated as another unsubstantiated rumors, because they don't want to attach their name to it. But surely no one bought shares for millions just to spread that info.

he explained to you why delaying NX by 4 months is a reason why they wont make as much money this fiscal year as originally planned, explain to me how your question is related to that.

You have to spend millions if you want to get a seat at the table we are talking about here.

They are majority share holders. Nintendo is a multibillion dollar company. (Yes, I said billion, not million)
You do the math.

And it's not a rule. It's business 101. Rich business men/women make informed business decisions. That's how they got there. Nintendo knows that as well. There's no reason they would withold information from their major shareholders.

So move it to the next fiscal year and make more money then...

thats not how it works, they would lose more money by not having new major products releasing. Thats sales from March-November that they are missing out on for no reason.

No reason? They could get even more software ready for launch and soon after.

Based on that logic, Nintendo should delay NX to 2020 because that gives them a further 4 years to develop more launch titles.

No, sitting on finished products for extended periods of time when your company needs new products to boost sales makes no business sense whatsoever.

At the moment Nintendo's priorities are most likely to avoid repeating the same mistakes as with the Wii U. Extended droughts for first party software are at the top of that list, hence no holiday 2016 launch. I think this is less about launch software than it is about the first half of 2017. Zelda would ensure a good 2016 launch, but that's not good enough when it's followed by a few months of emptiness in the release schedule. So NX gets delayed to avoid what happened to the Wii U. Nintendo will not want NX to get a negative reputation right from the outset, so the delay is the lesser evil between the two options.