Well, get some stuff out of the way:

• Yes, some games like Ghost Recon Wildlands, For Honor and probably Resident Evil sell more than Zelda, but only including PC-sales which we have no real tracking here.
• Horizon might have more sales digital included, but Zelda also sells on the WiiU, that included it is clearly in front.
• VGC is so far only at June 3rd, we are mid-July. The sales trends show Zelda in front of all four games (RE, For Honor, Tom Clancy, Horizon) at least on console, so the difference will be bigger one and a half months later.

So, Zelda is all facts considered pretty sure the best-sellign console-game. But why $300?

Well, Zelda so far is the only big game to choose from on Switch. There are multiple smaller games, but for most the only reason to get a Switch is Zelda. Because be real: no one is buying the Switch because the dock looks so beatiful in the living room. So basically everyone getting the Switch now, does it because of Zelda. That means, $300/€330 are added to the games cost ($70/€70). Another $60/€60 for the Pro Controller, which probably most Zelda-buyers purchase. That makes $430/€460 just for one game. As Zelda is also bought on WiiU I set the average price at the moment at around $300. You could also say $250. But it is pretty clear, current sales of Zelda are at a price-point multiple times that of usual games.

So, when Switch justifies a purchase later on with Splatoon, Mario, Xenoblade, Skyrim, Fire Emblem Warriors, Pokemon, Fire Emblem, Shin Megami Tensei, ... the price of the game drops to $70/€70. How much will it sell at the lower pricepoint?

EDIT: Well, as some don't seem to get my point I'll explain a bit more. Zeldas sales are in my opinion more impressive, because it is so far the only major reason to buy the console. In other threads this was pointed out by different people worded differently (Zelda has no competition yet), but that actually means that you have to buy the console to play the game. Competing games mean the console is bought for different games so it's price-point is relativated, but if Zelda has no competition on the console the console price has to be paid for Zelda alone.

im confused ...

So basically you said atm every Switch system is 'bundled' in every Zelda copy? I'm sorry I don't get it.

He's saying that BOTW is the only game where everyone getting it is buying the console for it. If you wanted to play BOTW, you had to buy a Switch, and no one owned a Switch.

Well, I'm saying that to play Zelda you need Switch. And you only buy a Switch, if you want to play Zelda (some exceptions aside). So basically yeah, you have to buy a Switch to play Zelda. Except you ot for the WiiU-version, which obviously not so many people do.

thats what games are for..right ?

Oh I see. But isn't that always the case with most of the launch exclusives? Sure some console offer more variety of games but you still have to buy a console if you want to play the games.

Yeah, sure. I only point a light on Zeldas sales from the standpoint, that the initial barrier in form of price is really steep at the moment.

It's also the best selling game on any system with dual detachable controllers.