The problem is that if you do anything to represent greater strength, they would also have a corresponding strength bonus to stat to represent that in the world. Otherwise you end up with "We are stronger, but not actually stronger."
On any particular world, there are rarely more than 5-6 PCs, out of tens or hundreds of millions of NPCs.
There's no reason, therefore, that
one halfling (the PC) in all those millions of people can't be as strong or stronger than a goliath. Especially when that halfling still can't use Heavy weapons or lift as much goliath can. The DM can
easily have every single NPC halfling have Strength 8 and every single NPC goliath have Strength 16. Having
one super-strong halfling doesn't break anything or make goliaths seem weak, especially in a fantasy game.
Practically speaking, Strength is used for
one thing: determining your attack and damage bonus. But it gives
exactly the same bonus as Dexterity does. A halfling with a Dex of 17 (+3) and a shortsword is going to inflict
exactly as much damage as a goliath with a Strength of 17 and a shortsword. But a goliath can use a
greatsword, while a halfling can't (at least not without a massive penalty). So even if a halfling has Strength 20 instead of Dex 20, that halfling is still not going to be doing nearly as much damage as a goliath can.
And even if you have racial ASIs, there's
still nothing stopping you from having a halfling with a Strength of 20. They just can't have it at 1st level, where a goliath can (if you roll for stats).
Plus, those ASIs
make no sense. Goliaths get +2 to Strength. So do githyanki, who are not only shorter than goliaths by a lot, but are described as slender. Centaurs get a +2 Strength, even though they have human arms. Mountain dwarfs are short but get +2 Strength. But loxodon, who are
bigger than goliaths and can on average lift 50 pounds with their trunk, get
no Strength bonus.