Rambam says in his introduction to Perek Chelek that the aggadot are all metaphoric. I do not take literally statements Chazal make about science which do not pertain to halachot. First of all, I do not think that they cared about a scientific theory if there was no nafka mina (in fact, the Baal haTanya opposes studying it where not needed for parnassa or to clarify one’s learning). Secondly, why would Ravina and Rav Ashi include purely scientific speculations in the Gemara? Thirdly, many things that are written about science are not literally correct.
Why did they do this? I once read a conjecture that they were making political statements that could not be expressed explicitly. It could also be that they were conveying deep kabbalistic ideas that had to be hidden from all but the most advanced. It could also be that they wanted to keep some things baal peh. In fact, I heard that when Rav Miller taught “Ein Yaakov” he would sometimes skip a portion and explain that he did not have a tradition for it.