FYI: OS X's grep is FreeBSD's bsdgrep. However, FreeBSD's default grep is still an ancient version of GNU grep (bsdgrep is only available as bsdgrep.).
Also, older versions of OS X used to have GNU grep [1]. So the more likely explanation is Apple's purge of GPL code from OS X. Since later grep versions use GPLv3, GNU grep was a dead end for them.
Unfortunately, FreeBSD's bsdgrep has some very annoying bugs (that are also present in OS X). No one seems to care about them, even when a patch is provided [2].
[1] http://opensource.apple.com/release/mac-os-x-1075/ [2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201650
On occasion I search for bsdgrep bugs, and did not find the comment / patch in [2]. Thank you for pointing it out, I'll look at it when I can.
I FreeBSD developer requested that I added a report to that bug [1]. After adding the patch to the report, I also reported this to the list [2]. I have also tried to contact the maintainer of bsdgrep with no luck. At some point you just give up ;).
[1] https://lists.freebsd.org/pipermail/freebsd-questions/2016-J... [2] https://lists.freebsd.org/pipermail/freebsd-questions/2016-J...