In other words OOP can be great for tooling, but doesn't make much sense for what R is meant to be used for -interactive analysis- in every day work. R's mess

In other words OOP can be great for tooling, but doesn't make much sense for what R is meant to be used for -interactive analysis- in every day work. R's mess of OOP systems works great, S3 is "fine" for just dispatching 'methods' based on attributes, one doesn't even know it's happening in base R ALL the time. R flexibility also makes it possible to build your own class system. i.e. modern ggplot2 has its own ggproto object system.