<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;The_Mythical_Man-Month#The_second-system_effect" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;The_Mythical_Man-Month#The_sec...</a><p>The authors decided to redo the underlying library.  And change the user interface.  And go cross platform.  That amounts to a virtual rewrite from scratch.