Nothing is entirely selfless. Yes, Youtubers are in it for the likes, subscribes and some money. No sin in that. But they're also giving the game exposure.
Unless someone does it so well that I want to pay for their time.
Youtube (aka Google) is a private company, so they have the legal right to restrict speech within their private establishment.
Youtube has the legal right to cut off their income, but it's a dick move.
Morally speaking, cmon Nintendo, just let them earn their little pittance. You're earning...
Copyright laws protect social criticisms (like reviews, parodies, analyses, critiques). So if the let's play has commentary, they aren't violating any Copyrights.