It ain't that difficult to understand.
In the current system that removes all ability modifiers to races... those who think large races should be stronger than small ones can easily have that by just not having small races point buy STR past a certain point. The small race player CHOOSES to accept the "reality" of size differential and just place their lower stats in strength. Same way they put their lower numbers into DEX for what they consider a "less agile" race. This can be done with no changes of the rules whatsoever. You can have weak halflings and unwise gnomes and stupid halforks all you want just by where you yourself place your stats. While at the same time... those who want halforks to possibly have really good INTs in order to play halfork wizard characters that are just as good as any other wizard can do so... also with no changes to the rules.
But why does this not work for people? Quite frankly I've always attributed to ego. Many D&D players across the board tend to want to play really, really smart. They want to play to the best of their abilities. And thus... if they determine there's a certain style of game they want (in this case, races having a bit of reality thrust upon them with their ability scores), they need the game to force that reality upon them. They need the game to say "Your halflings can't start with a STR higher than 15"... so that way if/when they choose to play a halfling fighter they can build it to be the best gosh-darn fighter they can make with the rules given, while still having their verisimilitude held up by the halfling being weaker than the halfork.
But if the game doesn't have that restriction... they have to purposefully choose to make a weaker build. They now have to go through the entire campaign knowing they intentionally nerfed themselves right at the start, and they will always have that bugaboo in the back of their heads every time things go sideways. They will always have that thought "Well geez, if I was at max like I could have been, maybe this whole problem wouldn't have happened." They didn't "play smart" when they made their character, they played to theme instead. And while losing the game while doing your best within the rules given is palatable... losing the game when you could have made better choices but intentionally chose not to is not.
And they'd rather force all other players to play like they do by keeping rules like racial ability score bonuses and/or penalties in the game.