[endgame]

Early GNU seemed to be very worried that people would go after them for copying proprietary UNIX source. The GNU Coding Standards at https://www.gnu.org/prep/standards/standards.html#Reading-No... suggest:

> If you have a vague recollection of the internals of a Unix program, this does not absolutely mean you can’t write an imitation of it, but do try to organize the imitation internally along different lines, because this is likely to make the details of the Unix version irrelevant and dissimilar to your results.

> For example, Unix utilities were generally optimized to minimize memory use; if you go for speed instead, your program will be very different.

So I think a lot of coreutils etc were written for extreme speed so there would obviously be no crossover with existing UNIX source.