Because both fight for the same audience: everybody. Whoever wins the game for everybody will beat the other and move it to a side corner. A little like FB and

Because both fight for the same audience: everybody. Whoever wins the game for everybody will beat the other and move it to a side corner. A little like FB and G+. Do you know anybody on G+? So even if it's better for 1:1 you can't use it, because the other 1 is not on G+. And currently it looks like everybody's betting on Instagram killing Snapchat in that battle.