They do have one, but if for the sake of consistency they stopped moving forward with the UI design just because of a few windows (which probably take more time and effort to change than it seems), we would still be stuck with a DAW that looks like Cubase SX 3 or Cubase 5, which look quite dated.
But they’re slowly touching things up where possible. Direct Offline Processing got rid of a few of the oldest windows in Cubase and I think you can expect more of that in the future.