Occam's Razor works most of the time. The explanations for most observed phenomena are a lot simpler if the world is round, if the Universe is expanding, and if higher life-forms evolve from lower ones. The observed phenomena can be explained within systems that believe the world is flat, the Universe is static, and that fossils have been planted in the earth as practical jokes, but it's messy. Why bother with trying to force a square peg into a round hole when there's a perfectly good square hole available?