The cable system also kept the rover and its instruments further below the landing rockets and their thrust, so the rover didn’t start its mission in a massive debris storm.
Around 3:55 in this animation with interviews:
https://www.space.com/16889-mars-rover-curiosity-sky-crane-landing.html
Those things added considerable weight, and so limited useful payload, and added considerable complexity.
I would have rejected that plan for a simpler solution.