I don't know if its cost or getting approval for the design but its up to the manufacturer. If you like the board you have to go with their decision.
I hate the wall warts. I do have some cables that are like short extension cords so the adaptor doesn't take up all the space on the power strip.
And always, ALWAYS have backups. Don't ask me how I know. OK you want to know. Middle of NY Harbor on a ferry for 4th of july Fireworks. My wire for the adaptor for my drum machine breaks right at the point where it can't be fixed. Had to keep going with just a piano. Worked out but taught me a lesson.