If Minecraft was FREE to Play is a video on ExplodingTNT's channel. In this video, Notch makes Minecraft free mainly because he needs more players to play basketball with him, but also to make Minecraft not so empty.
The main thing that stops people from playing Minecraft is the cost of the game. Whether you're playing on the PC, console, or even Minecraft pocket edition... you have to pay money to play. But imagine what Minecraft would be like if it was completely FREE to play! Anyone that wants to can play the game on whichever device they want. How crowded would the servers be?