I don’t know why this was downvoted, I agree that this is a highly unusual configuration. Why render to a frame buffer with 2x the pixels in each direction va the actual display, only to then just scale the whole thing down by 2x in each direction?
Because Apple no longer implements subpixel rendering for fonts?
Supersampling the entire framebuffer is a bad way to anti-alias fonts. Especially since your font rendering is almost certainly doing grayscale anti-aliasing already, which is going to look better than 2x supersampling alone. And supersampling will not do subpixel rendering.