Do you have any evidence at all that TAS videos help generate sales? Especially given they're almost exclusively done on pirated software? And honestly, we have no idea how many people would rather use that software then buy Mario Maker for $60. I've seen plenty of people use the existence of such things as a reason not to get Mario Maker. Again, I think this move is pointless, but I also don't think it hurts Nintendo in any way. And consider this, even if those videos had generated interest, it's no longer necessary now that the game is about to come out. Might sound a bit cold and unethical, but that's business for you
Do you actually need evidence that TAS videos help generate sales? Can you even chart that?
Many years ago FOX used to actively campaign to shut down any and all fansites for The Simpsons. Paramount did the same for Star Trek. They claimed it was "copyright infringement."
And, technically, they were right. These fans were using names, imagery, and more, all without permission. That constitutes the literal legal definition for a breach of copyright.
This was years before the "geek merchandising revolution." All these fans wanted to do was have a place to congregate with like-minded individuals, to discuss shared topics, and to stay up to date with news on their favorite TV show.
My point here is you can't choose your fanbase. You can't jerk your fanbase around on a leash. Eventually FOX and Paramount realized that it was better to embrace these people than try to control them. It doesn't matter if there's a direct correlation between (XYZ) thing and sales, because fandom is infectious. One fan becomes two fans becomes four fans.
Four fans fill out a wiki. Now you've made 16 fans. Etc.
Nintendo is taking something that doesn't actually hurt anyone and is demonizing it. They are being outlandish and controlling. They are creating negativity and pushing away the very same people who would support them. And worst of all, they are developing a reputation for this negativity.
If you can't see that that's a bad thing, then... I don't even know what else to say, really.