(2) Package names aren't always identical across platforms, at least not enough that you can rely on that.
It is a low-cost attempt to solve a problem that in my opinion doesn't really exist and it doesn't even do a great job doing that due to the points above.
For instance if you want to use pacman without knowing what -Ss stands for, at the slightest conflict, you'll be going back to using pacman without this wrapper.
Perhaps people who need to have package managers abstracted away could be a good target for Docker. Maybe a web UI to dynamically bake a docker image with required packages.