Because the BSD's are reflexively anti GNU.
nano(1) is GPLv3 last time I checked and that imposes more restrictions than most (all?) of the rest of the code in NetBSD. It is not about being "reflexive", it is a violation of the very ethos of the project. Gnu rejecting non-free licenses from their own distributions is not "reflexive", it is simply not in line with what they want to achieve and one should respect that.
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