It’s not really clear why Microsoft spent $2.5 billion on Mojang and Minecraft, a game most kids own already. But Microsoft chief executive Satya Nadella has given his own explanation: to get kids involved with math and science.

Yes, Microsoft sees Minecraft as a learning tool. Appearing at the Seattle Metropolitan Chamber of Commerce luncheon on Monday—because, what better way to address investor concerns than at a local Seattle luncheon?—Nadella was asked why Microsoft spent all that money. That’s 13.5 times the amount that Zynga paid for Draw Something, if you’re keeping score.

“If you talk about STEM education, the best way to introduce anyone to STEM or get their curiosity going on, it’s Minecraft,” Nadella said, as reported by Geekwire. “So I think what this open-world phenomenon will mean to the community at large, for people who builders, is pretty big, and we are very excited about the acquisition, obviously.”

“We are really excited about being stewards to the community that is Minecraft,” Nadella added.

Granted, you can build some amazing stuff i Minecraft.

That’s a little different than the tack Xbox chief Phil Spencer took when blogging his own reasons for buying Mojang—which, as he also pointed out, became the top online game on Xbox Live, with over two billion hours played on Xbox 360 in the last two years.

“At Microsoft, we believe in the power of content to unite people,” Spencer wrote. “Minecraft adds diversity to our game portfolio and helps us reach new gamers across multiple platforms.”

And for his part, Markus “Notch” Persson explained that selling Minecraft was about his “sanity.”

Let’s be clear—Minecraft certainly can be considered a learning tool. Although the whole point of the game is simply to survive, explore, and craft, a “free building” mode has allowed dedicated designers to create wonderful things: a working “hard drive,” computer, and more. In that regard, Minecraft is indeed a platform to allow kids free rein to express themselves creatively in a true “sandbox”—far more than other open world “sandbox” games like, say, Grand Theft Auto or the Assassins Creed series. And yes, it does straddle the PC, Xbox, Android and eventually Windows Phone.

But $2.5 billion for a game—and not even the most popular game, at that. On the PC, Raptr reported that a whopping 20.55 percent of all hours PC gamers spent in August were spent playing League of Legends, then World of Warcraft, then Defense of the Ancients 2 (DOTA2), followed by Counter-Strike. Minecraft clocked in at 7th, at just 2.24 percent of time played. Though Minecraft and Raptr's audiences probably don't overlap to an overwhelming degree—it's hard to imagine 10-year-olds signing into Raptr before launching Minecraft—skeptics are going to say that Minecraft is slowly fading from the PC.

Yes, Microsoft can use Minecraft as an envoy to other platforms. And Brad Chacos has some good ideas about how Microsoft can do that. But even with more than $85 billion in cash on hand, it’s just mind-boggling. $2.5 billion for Minecraft. $2.5 billion for Minecraft. Even a day later, it’s still hard to process.