It’s also how retina was implemented when it first came to MacBooks. Purists would say it’s how retina should work since any non-integer scaling must result in some small loss of sharpness and/or more GPU overhead.
To be clear you can have 2x retina today on any HiDPI MacBook just by setting the appropriate “looks like” resolution at exactly half the vertical and horizontal resolution of the panel’s native resolution.
However, most folks want “more space” than 2x retina, which is presumably why they upped the DPI on the new 14”/16” panels.