It is almost like they are considered a sub-race of humans, like Aasimar and Tieflings, and that humans are treated different than other races.
I mean... that's what the various plane-touched races are. Take a race, add planar energy, boom. My only complaint about them really is that it is very hard to make them seem like actually part of the race with 5e's design, but lore wise? Lore wise they serve their purpose excellently.
Subraces of humans with intrinsically different properties not related to culture doesn't seem like a good track to go down...