"Just a regular race that lives in the world and has cities and stuff" kind of doesn't work for a hidden menace. That's more cult side of things
I mean, we can apply that to anything. Do we really need elves? Just be an agile person. Do we really need dwarves? Just be a miner. Do we really need halflings? Just be short
But, well, those clearly have differences from being a human. And likewise, D&D has had those options for decades. This isn't some new thing, new race options go back longer than I've been alive
Goliaths are half giants, a highly popular idea from mythology that has far more justification for being in the game than halflings. They tie into that 'taller than humans' vibe and idea, and, well, I shouldn't need to really mention how common giants are in the game. If you want to play characters inspired by the paladins of Charlamange, for example, just being a big dude isn't going to work out if you want a proper Fierabras. Or, heck, you just want some giant-esque beings a bit more easy to deal with and on people's level, goliaths work fine
Goliaths are half giants. Like, this isn't a new thing, in both editions where goliaths and half giants have co-existed they've had basically the same stats, and they go harder into it in 5.5e with the variants that are blatantly inspired by the bigger giants. Just being a human isn't going to work for being, you know, a giant-kin who has the blood of the cold north in their veins and can call upon it
Would you tell people to just play human if they wanted to play a half-elf?