Did they ever give a reason for why the Tribals aren't a part of the NG+ experience?

[Tanis_Ebonhart]

I kinda liked the tribal stories and the group stories that required you get them to Bloodsworn up to Stormblood. Same with rebuilding the Doma place.

[Hyperia]

They will most likely do it eventually but as of right now, they have their plate full finishing the trust system and 7.0.

One complication to consider is that NG+ uses achievements to act as milestones for chapters. As tribes have only one at the end, it would be all or nothing.

[Iscah]

It could be that the way it tracks your quest completion makes it harder to temporarily ignore it or pretend it has been reset.

[Jeeqbit]

The reason is because they only put things into it if we ask. We were asked to ask if there's something we want in there since it seems quite clear that they can't just magick every single quest into there automatically.