The other big advantage IMO is that it straddles the space between "traditional stats package" (SAS, Stata, SPSS, Minitab, etc.) and "programming language". We here know that it's more or less the latter, but the "batteries included" standard library with first-class support for a "data-frame" type makes it feel much like the former, especially if that's what you're already familiar with. It's a gradual transition from a stats package to general-purpose programming, and you don't have to jump through hoops, install third-party packages for basic stats work, or deal with ugly/counterintuitive syntax.