I mean, it's never been impossible for a Halfling to have very high Strength in D&D. The only difference is whether or not it's the result of magic. Nothing stops a Halfling from putting on a Girdle of Storm Giant Strength or reading a Manual of Gainful Exercise in any edition. Gnomes didn't even have a Strength penalty in AD&D, and I have a Gnome Cleric of Flandal Steelskin in 2e who has 19 Strength because his God grants "+1 to Str or Con" as a granted power.
3e ushered in the ability to raise ability scores outside of magic, but for the most part, Small creatures took Strength penalties. 4e removed this, and even published a Small race that could have +2 Strength, the Svirfneblin. 5e didn't have Strength penalties immediately, tried it with Kobolds, many people didn't like it (I didn't really mind, since Pack Tactics was a neat ability), so it's only recently that we ended up in a game where ability bonuses were no longer tied to size or race (species?).
It's worth noting though, that in all these cases, nothing stopped a small creature from gaining great strength, it was simply a matter of time and opportunity. Just as nothing stops a Half-Orc from becoming Intelligent or Charismatic, or a Dwarf from becoming amazingly Dexterous.
I understand wanting ability scores to make sense, but they really don't. They are abstract because the factors they govern vary from person to person or creature to creature. In AD&D, there was this huge divide between 18 and 19 Strength just to create extra bonuses for high Strength warriors that really made no sense (and things got weird if you played a race with a bonus to Strength and you could just skip over !8.01 to 18.00!).
In 3e, thanks to the way carry capacity worked, a Halfing with a -2 Strength was actually proportionately stronger than a Human (Halfling gear weighed 50% as much, Halfling carry capacity was 3/4 that of a Medium creature)!
Even in our world, which has to obey physical laws, chimpanzee muscle exceeds human muscle in maximum dynamic force and power output by ∼1.35 times. And chimps, while not necessarily Small size, are smaller and lighter than humans on average.
D&D sidesteps all of these factors by giving you a simple ability score that broadly encompasses many related traits, despite the fact that these traits can vary from person to person in real life. Yes, it may not make "sense" that a female Elf can have a 20 Strength while a male Goliath only has a 15. It also doesn't make sense that dragon bones aren't as dense as diamonds to allow them to move swiftly and fly despite their massive bulk.
You'll note that these arguments can be flipped around, as the thread title suggests. "Why not have beauty as part of Charisma?" Especially if ability scores are abstract anyways?
My personal belief is that giving something for someone to point to and rate "oh that person has XX Charisma" is bad. I'm not even particularly happy with being able to point to carry capacity and jump distances as metrics for Strength, to be completely honest.
Have you ever looked at the build of an Olympic track and field athlete? We're told that Strength determines jump distances*, yet the mental image most people hold of a 20 Strength character probably doesn't look anything like a guy who can long jump over 29' in our world.
*yes, I'm aware the PHB mentions an Athletics check. But it doesn't tell us how that works, so I have no data to use to illustrate this point.
Ultimately, it's better to separate ability scores from how your character looks and keep them abstract. It's not that the Halfling is really a pint-sized Hercules, it's more that his or her player put more points into that aspect of the game. Trying to inject realism into ability scores undercuts the point that this is a fantasy game. If you want to play an adorable Halfling maiden that can lift a horse over her head like Pippi Longstocking, as long as everyone at the table is fine with it and having fun, go for it!
If your 17 Charisma Warlock is smoking hot, again, go for it! But I don't see how it serves anyone to introduce any element that could get people to think "you must have X ability score to play Y character" or "I'm sorry, you have 18 Strength, you have to be this tall, and have this much body mass to justify it".