I think this is originally to avoid any possible plagiarism claims by Unix--if a Unix tool was originally optimized for one of size/efficiency/speed/memory use, the GNU tools were optimized for one of the others. This is part of why the `yes` utility is so freakin fast in GNU, despite being kind of a weird use case for speed.
Mac builtin:
yes | pv > /dev/null
139MiB 0:00:05 [28.4MiB/s]
GNU:
gyes | pv > /dev/null
3.31GiB 0:00:06 [ 584MiB/s]