It's not like there was a time of plenty where all their leathers were made from oiled calf and now the well is dry. There were only a few issues where it was used and they weren't that long ago. I think gleam was one (2010) and then one after that... maybe there's more I'm sure kunk or other RO experts would know. RO is just not a brand that focuses on thickness or quality of leather used, it's more focused on design like many other designer brands.
And oiled calf isn't like some kind of amazing leather that should be put on a pedestal anyways. I've yet to see any calf leather oiled or otherwise from any brand that equals something as amazing as the horse leather used in lokesh's jacket. Though of course people look for different things in their leather. I'm sure there are people who prioritize suppleness... or even thin/paper-likeness in their leathers.