I don't know why, but Nintendo is able to focus on making Nintendo games exclusively, and they know their fans will support them and buy their games. They don't have to try and support other games as a strategy.
But for indie game developers with no following, I've heard it has been suggested that you offer to play other devs games to get them to play your game.
How did professional devs start? How did they gain a following? What actually strategies work?