And would be a big "f*** you" to the fans to just leave the story unfinished to reboot the franchise.
Don't mean to speak for all Halo fans but as a fan of the series since December 1, 2001 (when I got my original Xbox) I can say that Halo 5 itself was the biggest "f*** you" I could've been given as a fan. Again, I can't speak for everyone who is a fan of the franchise but it was just not where I wanted the series to go in any way (story or gameplay or multiplayer).
It wouldn't make sense to retcon what they built up already story wise by rebooting the franchise and never finishing the arc, but I don't think what they do with the arc to close it out will make people happy either.
On the bright side, it has made the long wait for another FPS Halo game so much more bearable considering how little I care now.