If it is a thing everyone can do, then it is not a way of doing associated with particular species. Like if everyone could get a breath weapon, then that really wouldn't be a dragonborn thing, even if they could take it too, would it?
Who is saying that's going to happen?
Also, there's an
enormous difference between saying "this particular halfling is pretty darn strong" and "anyone can take any racial trait they want."
This to me is really unconvincing. And If you feel that the rules for PCs don't need to reflect the reality of their species in the setting, why on earth would this logic only apply to ability scores? Why can't my halfling have breath weapon and my orc brave trait? You still could have all the NPC halflings not have breath weapon and all NPC orcs not have brave. So if PCs are not bound by their species why we have dedicated race splats at all ? I don't get it.
Because ability scores are
already variable. Any PC can have any stat be anywhere from 3-18 (or 8-15, without point buy/stat array) before ASIs. Those numbers are all over the place. Even the complete average PC has stats in the 9-11 range, which is still variable. If you roll low on the dice, you can stick it in your "racial stat," if you want,
and that's always been allowed. If you roll high, you can stick it in your racial "bad" stat, which is also fully legal.
These have literally been the rules since the very beginning of D&D, and once 3e started and there were no more racial stat minimums and maximums, then there has never been anything stopping you from going as high or as low as your dice or points allow, even if you don't favor your "racial stats". You can, legally, have an orc with Strength 3 and Int 18.
But racial
traits are
not variable, and never have been. Every orc in 5e has Aggressive and every halfling has Lucky (or whatever they're changing the names to). There has
never been any official rule saying that a PC can choose their racial traits from a pool available to all races. Maybe in that 2e Skills & Options line, but that itself was super-optional. Even Tasha's doesn't let you pick from
any racial trait; you can only choose a feat (and you technically can't pick a racial feat, since you're not technically a member of that race).
So do you understand it now? Because attributes are already varied, it's fine putting a +2/+1 in a varied attribute.
Also (in case that's not enough), a +2 in one stat is pretty much balanced against a +2 in any other stat. If you put it in Strength, then chances are you're playing a fighter, barbarian, or paladin, and maybe a ranger. If you put it in Intelligence, then you're likely playing a wizard or artificer. Etcetera. You're not going to be OP if you put the +2 in a different stat than the one your race says.
But racial traits aren't balanced against each other. That's why some races have one or two traits and other races have three, four, or more. If you swap out a halfling's Nimble for an aarakocra's Flight (even the new, 30-foot version), then you've unbalanced your character because you still have all Lucky, Brave, and whatever your subrace trait is.
Sure. You chose the one situation where the dex and strength builds are closest to each other, but different weapons still result different imagery and their different ability scores affect different things in other areas. The goliath will be better grappler, the halfling way stealthier. The halfling will use shortbow as their ranged weapon, the goliath a handaxe. These characters will play differently overall, even in combat.
Would they? I imagine halflings as using slings for their ranged weapons, as was the norm until slings became a simple weapon everyone could use. I can't see them as using even shortbows since, y'know, short arms. They can do it by both RAW and RAI, but it's hard for me to picture it. I picture goliaths using spears, or just throwing rocks like a real giant, and only tossing an axe as a last resort. And I picture halflings as being grapplers as well. Leaping onto someone's shoulders, covering their eyes and mouths, etc. They might not be able to keep someone from moving (and inflict the Grappled condition), but hey, Level Up has rules for such things where D&D doesn't.
So see, different weapons still result in different imagery--but you and I have different images.
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