somehow this is acceptable for elves... but I totally understand the problem.
So maybe for humans don't change ability scores, but rather alter purely physical traits like heat/cold resistance, wings, being part undead, being an aquatic race (with Aquaman being a thing, one could have easily come up with an aquatic human race)
As much as I like elven subraces, I don't like the fact that only elves are the ones who need a subrace for every little schtick just because elves are so widespread in folklore and literature.
And "humans are ALWAYS and ONLY jack of all trades" seems a bit lame... (and yes, i'd totally play a winged human. Or orc.)
To be fair, I always thought tieflings, aasimar and genasi were human subtypes, and that the underlying magical assumptions of the D&D cosmology suggests that humans are all racially identical for stat purposes.....except when something magical changes them, often by birthright.
To look at this from a more metacultural perspective, it's pretty easy for us to all agree that one reason you don't start assigning statistics to human racial groups is because A: it's a creepy judgement and how do you quantify this, let alone justify it, from a mechanical or scientific perspective when our own human experience already tells us that the real world does not work the way D&D mechanics do, B: it's uncomfortably close to the false science of past eras and fringe groups today who want to make those judgments; and C: even if this were culturally okay for some reason, actual science indicates that there are not, in fact, racial differences that can quantifiably be identified, let alone applied using D&D mechanics in a narratively coherent fashion.
Or put another way: if I were Inuit and you told me I get cold resistance, I'd laugh at you. (EDIT: But per othr post, if you told me I was of the Winter Ice Men and my goddess had gifted us with cold resistance, I'd be like....cool, sign me up)
Anyway: D&D as I said already does this, and it does this by adding magical elements to human types which makes them more than human, and also magical. Once magical, the rules suddenly make more sense and anything goes, pretty much.