It's the same as the whole multiple Godzillas and multiple Ghidorahs thing. One got chosen to represent the whole.
I stopped reading here. None of the Ultras are attempts to reboot Ultraman Hyata. UltraSeven is completely different from Ultraman. Ultraman Jack is different from Seven. The fact that the ultra warriors all appeared on screen at the same time, as apposed to Showa and Heisei Godzilla, is the fact they're different entities entirely.