For me the release tempo was too slow during a major gui transition a few years ago, so I learned how to compile it with the help of many folks here and GH. The procedure has been further refined and committed to the repository. I still use the software, and still build and share the builds I make via the rawtherapee.com team and Direct download links to the latest RawTherapee development version.
Larger organizations can provide breakaway release teams without freezing development, whereas the smaller RT group really focuses primarily on getting a few very well-documented release candidates out to beta testers. With the Local Adjustments quantum-leap in 5.9, there is no wonder two years has already elapsed, even in the face of being already many years in developement with almost no gui!