For me, these racial adjustments reflect some average difference between races in the fantasy world.
Dwarves, on AVERAGE, are stronger than other races.
but in the case of a HERO of this game, the protagonist, you could be the strongest deep gnome ever, the Warrior champion of the Deep Gnomes, and start with the +2 to STR.
Maybe your top STR will not be as high as that of the strongest Dwarf, so maybe your limit should be around 20, at least 2 less than the limit for dwarves.
but I don´t think D&D 5E deals with that...right !? Does a Half-Orc have higher upper limit for Strength than a Human or Elf ?!
I doubt.
Larian´s approach is precisely the opposite! Let people focus on character build, on choosing the race they want to enjoy more..not worrying about another +1 to specific abilities.
I like Larian´s decision... you can play the most charismatic Dwarf, the wisest Tiefling, the strongest Human.
You are the protagonist! not the average individual in Forgotten Realms.