I'm not very fond of the "you people" here, but perhaps I can explain how many that feel that options should have justifications feel.
To put it bluntly (and fairly extremely): If a race/class/whatever-part-of-D&D doesn't justify it's existence, it may as well not exist. If a race acts like a human (diet, culture, language, etc) and looks like a human (more or less), it may as well just be a human. It doesn't matter if they have rainbow hair, green skin, or are covered head-to-toe in shaggy hair, they may as well just be a human. Sure, real world humans can't naturally have rainbow hair or green skin, but that doesn't matter in a fantasy world, where literally anything is possible.
However, if there is something else to further differentiate the races - maybe the rainbow-haired race is actually a subrace of Aasimar that are descended from Unicorns, or the green-skinned race are actually photosynthetic and have a bond with nature (probably being dryads), and the overly-hairy people are actually Bugbears - then that helps "justify" their existence.
Sure, this isn't needed. It's a perfectly fine and valid way of playing D&D by having 70 different races for humans that act like humans and look like humans in everything but minor cosmetic differences (unnatural skin/hair/eye color, hair on unnatural parts of the body, language, minor mechanical differences (like size), etc), but that's not what many people prefer in their games. I like my world-building and homebrewing to be more in-depth than "another human race, but with purple skin" or "a homebrew class with innate arcane magic (like the Sorcerer), but it's a Half-Caster". I'd be fine with an Arcane-Half-Caster similar in theme to the Sorcerer, or a race of people that look like Humans but with Purple Skin, but there has to be more to them than just those minor differences (Felshen in my world often have vibrant purple skin and other multicolored skin tones, like cyan, cream-orange, turquoise, and so on, and their psionic nature sets them apart from just being "multicolored humans").
The same also applies to creating new animal races. If Lizardfolk already exist, I don't need Crocodilefolk (Lizardfolk mechanics already work perfectly for crocodile people), Dinosaur-People, or Tuatarafolk. If Grung are playable, I don't need playable Grippli, Bullywugs, or Toadfolk (okay, I will admit that having one broader frog/toad-folk race with subraces for Poisonous Frogs, Toadfolk, and Wolverine=frogfolk would be cool). If Aarakocra are playable, I don't need different races for Hawkfolk, Eaglefolk, and Falconfolk. If Tabaxi and Leonin are playable, I don't need Jaguarfolk, Tigerfolk, and Ocelotfolk. (There are some animals that do deserve their own separate races, even though the concepts have some overlap, like Owlfolk and Aarakocra, Leonin and Tabaxi, Lizardfolk and Dragonborn, etc, but there is a line that has to be drawn to avoid crazy explosions of every different "animalfolk" variety of different types of birds, reptiles, and mammals.)
And I absolutely love stuff like this! It makes Elves seem unique and cool, and also helps inspire how to roleplay an elf (for both DMs and Players) differently from humans! The "I don't need to sleep, so my race is Diurnal" is an awesome hook for a reason to roleplay an elf! This is kind of thing is exactly what I'm asking to be more common in D&D races! This isn't even setting-specific, although it's specific to the elven race!
Dwarves have a low center of mass and they live underground, so they sleep standing up, Forest Gnomes are friends with nature fey and small animals that can alert them if enemies arrive, so they just take naps in the middle of the forest, curled up with a blanket of moss, and stuff like this creates a lot of really fun and interesting bits and pieces of the races that you can use to further differentiate one from another. Humans can't be as diurnal as elves. They (typically) can't sleep while standing up. They can't just face-plant out in the middle of a grove without fear of pests or predators disturbing them. These kind of things help give the races more unique identities, and are exactly the reason why I created this thread!
Of course it may suggest the Drow retain the natural elf skin tone and other species are unnatural 
