They implemented it. They just couldn't get out of their own way to successfully sell it (See "Dealer's of Lightning"[0])

0 - https://www.amazon.com/Dealers-Lightning-Xerox-PARC-Computer...

No that is not true. Read about PARC and all the crazy tech they built some time. It was ahead of its time!

They changed the live system from having line by line scrolling to pixel scrolling after Jobs asked why they didn't do it during the lunch break.