Welcome to Dungeons & Dragons, a game where you can be a great hero, from a fantastic world, doing unbelievable things. How do you want to play? You can be a short strong Dwarf, a wise graceful Elf, a huge and powerful Dragonborn, maybe a small clever Gnome, and we haven’t even gotten through the Core Rules!
You want to play a Human? Why? In a game where you can be anything, why be something you can be in real life?
Because they are Diverse, and they offer great Contrast.
The simplest reason someone might play a Human in D&D, is because they offer the most choices. In the Player’s Handbook, as well as most settings, each race has a particular culture, and fulfills a particular role both in the world, and in the party.
Dwarves might be from below the mountains, have an affinity for weapons and gemstones, have strong ties to their family, and follow the “Work Hard, Play Hard” model. This isn’t true for everyone that plays Dwarves, and this isn’t true in every setting, but it is extremely common, and if players want to play that kind of character, they tend to fall into Dwarf.
Elves might be from the forests, are agile, wise, see the beauty in nature, and see the quick reactions of human to be impatient and reckless. Again, not a guarantee, but a very common trope.
Tieflings are great when you want to stand out from a crowd, follow that “I don’t belong here” trope, and have a strong stereotype of being Chaotic Bisexual. Certainly not a bad thing, and definitely not every time, but a common trope.
Humans, in most settings, don’t have such stereotypes. They aren’t always one thing, because we, as humans In Real Life, know that people aren’t all one thing. There isn’t a single culture that defines us. You can take any character concept, replace the Race with Human, and very little would actually change, especially since you can keep the Ability Score Improvements with a Human Variant. No matter who you want to play, you can almost always achieve the same thing with a human.
However, I think the biggest reason why someone might want to play a Human in a fantasy world, is because it highlights how different everyone else is. I think I can confidently say that in most D&D settings, Humans are the most prominent race. They either have the highest population, take up more of the ruling class, or are generally seen as the default race of city guards, unless otherwise specified. This serves a secondary purpose, of letting the PCs stand out not just based on their actions, but on the fact that they have pointed ears, short statures, tails, or horns. You feel extra unique when you can be picked out from a crowd, just by your silhouette.
So, when a Player chooses to be a Human, they are giving the added benefit of each player feeling unique in their own party. Sure, if there’s no humans, you might still be the only Dwarf, but next to a Human, you exemplify what makes Dwarves unique in terms of what the Players can relate to.
Also, there are two types of heroes, usually, in the stories we tell as a culture. There are the Larger-Than-Life heroes, who are things we could never be. The Superman, the Thor, the Witcher, the Luke Skywalker. These are people who are beyond human, they are extraordinary simply by the way that they exist. Then, there are the relatable heroes, the ones that we can see ourselves in, and are inspired by the way they interact with their world, with such bravery and inner drive. The Batman, the Black Widow, the Ciri, the Han Solo. These people aren’t magically or supernaturally gifted, they are human, who push themselves to be great. Sometimes it’s fun to play that character too. A Human, in a world full of races that live longer, have fangs or horns, have inherent magical ability, it shows just how much you’ve worked to be able to stand by their side, and be considered an equal.
Being a Human character isn’t boring, just because you are Human in real life. It helps show just how fantastic the world, the party, and the character themselves, really truly is. So when you want to Roleplay a Human in D&D, play it honestly, whatever that means to you.