There's a simple, obvious reason why 'Fortnite' is the biggest game in the world right now

More than just being a fun, unique game, there are two really obvious reasons why "Fortnite" has become absolutely dominant:

"Fortnite" is part of an emerging category of games that offer a premium experience with zero up front cost. The game is of course making money otherwise — somewhere in the ballpark of $225 million in March alone, according to analytics firm Superdata.

Here's how an unknown game with a unique premise rocketed from obscurity to stardom without charging a dime.

"It's how it can go viral — it's so accessible."

The man at the top of the "Fortnite" wave is a Twitch streamer and professional gamer named Tyler "Ninja" Blevins — the quote above is from him, speaking with the H3 Podcast in a recent interview.

Being good at a game and helping fans learn how to get better is a common theme among Twitch streamers, but Ninja has captured the zeitgeist with his streams. Since anyone can play the game, and it's relatively easy to learn the basics (third-person shooting), over 40 million people have already jumped in.

And where do those people look when they want to improve? They look to Ninja.

He's making somewhere in the realm of $500,000 monthly playing "Fortnite" on his Twitch streams — and that's before we talk about the many other revenue streams Blevins operates.

He's making all that money from being really good at "Fortnite" — a direct translation of his longtime skills as a professional gamer. One main reason people watch Ninja is because he teaches them how to be better at "Fortnite."

"Fortnite" doesn't feel like a free game.

It's difficult to put a finger on exactly what it is, but there's a subtle difference between most paid games and most free-to-play games.

Part of it is expectation: If a customer pays $60 for a game, they expect a polished, immersive, expansive experience. On the flipside, paying nothing for a game lowers the stakes dramatically. If it's bad, the only thing you've wasted is your time.

In the case of "Fortnite," it doesn't "feel" as vacuous as so many free to play games do. There are no timers stopping you from doing certain things, only accessible by paying to speed them up or waiting hours of real time. Quite the contrary: "Fortnite" feels like a premium experience.

There's a good reason for that — "Fortnite" was in development for years, being built as a tower defense game (now known as the "Save the World" mode). The free mode that everyone is playing, "Fortnite: Battle Royale," was built on top of a long-in-development, highly polished game.

It "feels" like a premium game because it's basically a premium game.

"Fortnite" is on everything.

Own a PlayStation 4, or an Xbox One, or a PC, or a Mac, or an iPhone/iPad?

If you answered yes to any of those, you're able to play "Fortnite." And that accessibility is huge for growing player numbers. If you're even remotely interested in playing "Fortnite," chances are you can — today.

Maybe your friend is playing on their iPhone, and you like playing on another platform? You can probably play together! The game allows players on various platforms to play together (with the exception of Xbox One and PlayStation 4 playing together — that doesn't work).

Between being free and being everywhere, it's really easy to say yes to "Fortnite" if you've never tried it before. And that's huge.

So, how does "Fortnite" make so much money if it costs nothing? Simple: By selling stuff!

You could download "Fortnite: Battle Royale" today on your PlayStation 4, Xbox One, PC, Mac, or iPhone/iPad. It costs nothing to download and play. And you could never pay a cent for the game, simply enjoying the free experience.

Pretty sweet!

Alternatively, you could become one of the tens of millions of people obsessed with the daily/weekly/monthly/seasonal grind of the game's "Battle Pass," a system for leveling up your character and earning sweet unlocks. In a brilliant move, you can play "Fortnite" for free in perpetuity — but if you want to unlock sweet, sweet loot, you have to pay for the game's Battle Pass.

More simply: Playing "Fortnite" is free, but progressing through the game's loot-unlock system is not.

You can outright purchase in-game currency as well ("V-bucks"), and use it to buy in-game stuff. But none of that in-game stuff offers an advantage over other players — it's strictly cosmetic. Maybe you want a sweet outfit for your character, or a new dance move, or a different looking pickaxe.

BONUS: There's one other major reason that "Fortnite" has blown up even larger than its main competitor, "PlayerUnknown's Battlegrounds." Can you guess what it is?

"Fortnite" and "PlayerUnknown's Battlegrounds" ("PUBG") are both the same type of game: Battle Royale games.

These are shooters that pit 100 real players against each other in a winner-take-all match to the death. And, on paper, they're very similar games.

In reality, the differences are stark, and the most obvious difference is entirely visual: "Fortnite" is a cartoony, visually pleasing game. You might be blasting people with shotguns and assault rifles, but it feels like you're shooting paintball guns at the absolute worst. When another player "kills" you, there's no blood — you simply disappear from the world as the game transitions from showing you where you are to following whoever took you out.

On the contrary, "PUBG" is visually dreary, and serious and ... distinctly less fun as a result. It's a subtle difference, and one of several that distinguish the two games from each other, but it makes a big difference in reality. I'm, personally, far more inclined to spend time in the silly, colorful world of "Fortnite" than the post-apocalypse sadness of "PUBG." And I doubt I'm alone in that feeling.