R had a good run, and IMO they still have some packages that are just too good to see it languishing into the future, notably the package data.table. I have not come across a better library for data manipulation, in R or Python. The syntax is excellent and it is faster than most alternatives, especially the popular ones.
I think an important factor that contributed to R's downfall is the decreasing hype around data science, as well as the fact that the core base of R users do not have a background in the STEM fields, but rather the humanities and social sciences. I do believe that the R community of developers are dedicated and perhaps, in relative terms, are more involved with their projects than a typical Python developer. But that's not enough, the sheer numbers of Python developers eclipses R's and that is too hard to overcome.