There are playable races for a number of monsters, for example you can play a Bugbear, Duergar, Goblin, Goblin, Hobgoblin, Kenku, Kobold, Lizardfolk, or Orc, and Satyr all of which are directly available as monsters.
Some features of the playable races differ from the traits the monster has. For example, for the Goblin, both are small, have a speed of 30 feet and 60 feet darkvision and Nimble Escape, and the playable race gains Fey Ancestry and Fury of the Small in additon. In many cases, the playable race is like this: it emulates the monster's traits, and adds some extras.
Others have wondered why, or if they should not rather be the same? My take is that it would be nice if they could, but the game designers were looking to make the playable race more interesting and to play better, so that is not really my question.
What is more interesting to me is how to explain it in-universe. I think you can justify it by claiming that the player characters are special. Not everyone gets ability score increases like the PCs do either — the commoner of any humanoid race has just flat 10s across the board. Being special may translate into additional abilities, or even be the lack of a common ability.
Still, that several PCs of the same race would be special in the same way may be harder to suspend disbelief on, and explaining away the differences feels off, especially when the features are very different, like for the Kobold — all kobolds are sensitive to sunlight, but somehow the PCs are not.
For Kobolds, both the race and the monster are small humanoids with darkvision, and 30 feet speed, but the monster has Sunlight Sensitivity and Pack Tactics, instead of the race (Monsters of the Universe, p. 25), which
gets a Draconic Cry that gives both them and their allies a benefit similar to Pack Tactics a few times per day,
gains Kobold Legacy for their pick of a skill proficiency, cantrip, or advantage on saves against being Frightened, and
lacks Sunlight Sensitivity.
My question is: would it be balanced to instead of Draconic Cry and Kobold Legacy give the kobold race Pack Tactics and Sunlight Sensitivity?
