So one day I was playing Super Mario Galaxy, and I reread the story. The Comet only comes by every 100 years, so I wondered how both Galaxy 1 and 2 could be canon. Then it hit me. Galaxy 2 is a retelling of Galaxy 1. Then something else hit me. Every main Mario game has been a retelling of the original Super Mario Bros. This explains why every game feels the same. It is the same, just told by a different person. The story changes a little with each telling, but the main plot is still the same. But hey, it's just a theory.