Two different systems; on the mod side there are two different UIs (one to set each) as well. Yeah it's weird.
But what I thought was funny was, if you didn't know that, it would look like the two "experiences" were tailored separately: OG redditors get the constructive messaging in the spirit of RMS's mission, but modern social media redditors get the modern social media simplified passive consumption.
I suppose it's a consequence of the current mods having been immersed in that modern social media environment for longer.