For one, I don't know of any theories in science that are justified on simplicity alone.
Also, simplicity will never add to the *LIKELIHOOD* of a hypothesis. Rather, it adds to the overall *probability*, and is for this reason known as a 'superempirical value' among philosophers of science.
To clarify this point, i.e. to clarify the jargon, say we have two empirically equivalent hypotheses, i.e. they explain the data equally well. Because for each thing one theory explains the other does as well, we say the theories have the same *LIKELIHOOD*.
Simplicity adds to our probability which also takes into account either our subjective degree of belief in the hypothesis, or its rating in terms of pragmatic values like SIMPLICITY, PARSIMONY, CONSERVATISM, etc.
Flat Earth is obviously less parsimonious since it considers all the planets to be created by the same astronomical principles, and result in a less diverse array of different planets. If FE claims that they see the universe radically different, then CONSERVATISM is on RE's side. To overcome the influence RE has in pragmatic value's, FE will have to explain AT THE VERY LEAST one additional and agreed upon piece of observed data. SO FAR THIS HAS NOT BEEN DONE.
FE'ers, like Mr Username and Ms Bishop, are basically just ejaculating their emotions toward the way they'd like the world to be. They have not shown it the way scientific inductive logic asks of them. If they cannot do it, so much the worse for FE.