The reason why Minecraft is a Popular game is because it has a lot of playability and you can design what ever you want. In SinglePlayer you can play and design anything your heart desires from being a house to Becoming  a Mansion, or a village to a Town then a City and you have so much to do. In SinglePlayer you can build maps that you can post and peopele can see it and play it as well. MultiPlayer is a Different Story, Multiplayer is playing on Servers with your Friends and play Minigames on servers too. But in Multiplayer you can Explore maps and Games that people have made and this gets you excited as well, when you see your friend and play with Him/Her You just want to play with them and have fun. But Overall Minecraft is a creative game for Children and Adults, and it is to Show that what ever they think of, They can just Put it on a Computer Screen and Show it to the World. This is why Minecraft Is a Popular Game.