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...
0 - https://www.amazon.com/Dealers-Lightning-Xerox-PARC-Computer...
It's not clear to me how much it cost them to build the Star, but it might have been pretty close to that 20000 figure if they included all the R&D costs that went into it, and the fairly specialized high end hardware at the time like 20MB HDD. And it was being done in fairly low quantities so not much economy of scale.