There is legitimately an issue in all fantasy games where designers build a rich diverse setting with many different races that have their own exciting cultures and designs and differences, but if they include "human" about 50% of players choose human. This persists through boardgames, RPGs, videogames and LARP. The exact proportions vary a bit from game to game and from playerbase to playerbase, but it's very common.

Larian revealed some stats a while back for BG3, about 50% of players chose human, elf, or half-elf (the three most "human" looking races". If you choose one of the existing characters to play as, Gale is the most common. It's an encouraging result, there's more diversity in the picks for BG3 than most other games, but it's still very "human" skewed. Halfling, Gnome and Gith were much less commonly picked.

If you've been tabletop gaming for a long time, your instinct is to think things like "but why would anyone play as a human? that's boring!" or "I play these games for escapism and I want to play as something different to myself." or the like, but the reality is that there's a very large cadre of players who want to create characters or avatars that are "like them" - they want to self-insert, or they want to pretend they are their character, and have difficulty squaring that with being a gnome or a goblin or a Dragonborn.

As such, you can get this weird disconnect between your setting writing (where there's a large variety of different, interesting races in the world) and your playerbase (majority human) which skews your design towards a human-centric viewpoint that you don't necessarily want - especially if you put work into the design of cultures of other races, and you want players to explore a variety of ideas and styles.

So what's the solution? - a common design solution is to mechanically incentivise players to choose outside of human, by giving humans disadvantages, or giving other races unique advantages that are desirable. Is this the right approach? your mileage might vary, but it's one of the easiest "patches" to encourage diversity in the playerbase, so it's a common choice.

Does 5e do this? probably not - human is very mechanically powerful, especially at low levels where the variant human feat can make a big difference... but they did make humans more "boring" than the other races, hopefully encouraging more dragonborn and gnomes and half-orcs and so on.