I think they do it this way because it streamlines development. I don't know exactly what changes with wrapper vs. non-wrapper, but I imagine that using the wrapper reduces the amount of redundant code that they have to maintain across all of the plugins.Would be nice if there was a simple way of unwrapping the wrapper and getting individual component, vst and vst3 files. You know, like nearly every other plugin....
I've encountered a couple of non-DAW hosts that can't even properly load Waves plugins because of the wrapper, so it's definitely a pain from a user perspective.
EDIT: I think shell is actually the technical term for what they're using, not wrapper.