You're not the sole project to adopt XenForo despite being FOSS (0AD is a good example), but most FOSS projects choose Discourse or phpBB specifically to avoid depending upon proprietary software.
I think it's all in the last sentence: why avoid depending on proprietary software in the first place when said software can get things done? In my opinion that alone gives you a good first impression as to what the generic FreeBSD mindset really is: "
The power to serve...", but
without discrimination.
I'm not just saying... take the ports collection; you'll find plenty of closed source and/or even commercial software in there. That, to me, is
exactly what FreeBSD is all about... we (generally) don't bother with (IMO lame) politics but would rather focus on functionality,
tech; "stuff that works".
Of course that's also only so much true... even though it's not activelly shunned there's always been quite a move to keep GPL licensed software out of the base system, to my knowledge this was even a main force to replace GCC in favor of Clang (a move I quite actively supported myself by being an early adaptor, documenting my findings and I think I even wrote a few guides on how to set up Clang / LLVM before it became official). But once again... no 'discrimination': if you want to keep GCC around or even replace Clang with GCC then you can, even today.
This is just my 2 cents, but if you're so worried about "politics" that you'll even let it affect decisions which directly involve functionality then... maybe it's time for a more impartial look at things. And well, why change for the sake of change, makes no sense to me.
As for Xenforo... I've worked with & administrated many fora software myself, and well... Xenforo has very specific features that others simply don't have. Generally speaking its maintenance is also
a lot easier and even more streamlined. Not to mention feature friendly.
Fun fact: I've had a (friendly!) interaction recently with an anonymous moderator about "something" which I thought needed their attention.
However... I also responded to that situation in a way I always do. Lo and behold: several days later I even got some extra feedback about the afternath of that situation. That's a feature PHPbb simply doesn't have, and it really makes a difference I think. Let's just say that reports have real meaning here, and it can show.