My cynical take: Roland had a product that wasn't selling well, so they created a stripped-down version and instructed their subsidiary to bundle it with SONAR as a form of advertisement. Sort of how Dell computers come with a bunch of useless pre-installed crapware.
My less-cynical take: Cakewalk needed something no competitor had, so they went to the parent company and asked "what's the coolest, most unique thing you've got?" Let us put it into our next version so we can have a unique product differentiator. Granted, no one's asked for it, nobody's even sure what to do with it, but Studio One, Ableton, Cubase and Reaper don't have it!
Why they didn't ask for an updated V-Vocal (also a Roland product) instead is a mystery.