For me, it has to do with the fact that most cars, maps and content in general was made around that version, so most, if not all of the stuff works flawlessly. I have no experience in the matter but I do remember when content for 0.4 was starting to come up, it was labeled exclusively for 0.4. It wouldn't work, or have multiple issues with the previous version. I really don't know what issues did 0.38 present for it to be replaced by the new version, but for me 0.38 is the best ROR to date.