Just to add some information on this:
There are various reasons why studios may not want to release a video on the SLR platform. The Riley video was tracked on /XVR reddit and /OculusNSFW for some time. When it was released, the feedback was predominately negative due despite the actress being prolific. My understanding is that they had technical difficulties with the shoot and the camera was off target, resulting in a blurry experience where you couldn't really see Riley's details.
VRB is one of the first studios to adopt 6k, while positions in some of their videos have been hit or miss for me the picture quality has been some of the best so far. It may be that the studio did not want to bring a video that didn't meet their quality standards to SLR, which currently is the "Netflix of VR porn."
Other examples of omitted videos include the newest Nov 7 2018 release by JustVR -which is one of my favorite studios. When I checked the JustVR site I found that their latest video was a 3 way featuring a TS girl. While this is cool with me, I understand that TS porn is not everyone's cup of tea and that is probably why it wasn't released on the mainstream platform.