Really what this comes down to is that, in real life, many of the actions D&D associates with "agile" characters, actually require a host of different physical abilities. I mean, in real life, there are many different applications of strength and it's perfectly fine to be good at one and not others- Olympic runners have powerful legs, but they don't exercise their upper bodies as much because the bulk would slow them down.
Female gymnasts weigh very little (under 120 pounds, I believe Simone Biles is 104), but they are typically stronger than the average man to be able to perform.
D&D has evolved into a system where characters are incentivized to focus on either Strength or Dexterity. A Fighter can be an effective combatant with very low Dexterity, as can a Rogue with very low Strength. However, the actual feats you'd expect a Rogue to be able to perform may, in fact, require at least above average Strength.
As a side note, D&D's jumping rules are completely inane as well, as they only take athletic ability into account at the DM's discretion, and giving incredible leaping power to the strongest humans, forgetting the fact that the strongest humans have a lot of bulk which would affect their jump distances or heights- the strongest man on Earth currently weighs 434 pounds, while Mike Powell weighed just under 170 when he set the world long jump record.
To steal a phrase from another poster, this creates "cognitive dissonance" where the mechanics of the game do not reflect reality.
D&D evolved to allow characters to specialize in key ability scores and to need other ability scores less. However that's not a luxury real people always have when they choose to excel in particular fields of physical ability.
In the case of the Rogue, they do have access to things like Expertise that help them with this- Expertise in Athletics is more valuable in the long run than a 20 Strength for the purposes of making checks. But obviously, not all the rules work nicely with this conceit.
The Athletics/Acrobatics divide is especially egregious when it comes time for a DM to decide which ability applies and when. As noted in this thread, some climbing is Strength/Athletics, but other forms of climbing can easily be Dexterity/Acrobatics.
The point:- D&D is built to incentivize you to not make realistic characters. If you want to be a Parkourista in real life you need Strength, Dexterity (and Constitution), Athletics, and Acrobatics. In D&D, if you want to be a Rogue, points/good scores put in Strength have diminishing returns over other ability scores, incentivizing you to create a potentially unrealistic character.
You can attempt to solve this by changing what ability scores mean and how they are used, but that only makes the cognitive dissonance worse, not better. You can give classes more special abilities to let them ignore the fact that there are 6 ability scores, but then you beg the question of why you need six ability scores in the first place.
D&D is not a good model for verisimilitude. For all the lip service is pays to the concept, it is a game first, and many of it's assumptions and conceits are based on the idea of making it play well as a game. There are going to be things that make no sense in reality. Once you go down the path of trying to change things in order for them to make sense, there is no end. At some point you have either made an entirely new game, or you leave something in the game you can live with, that still makes very little sense.
The easy solution is either to accept that a 10 year old kid with a 7 Strength can take levels of Monk and beat a grown man to death, or kill abstractions that allow characters to "get by" with some low scores, leading to weaker characters overall (unless you use increased point buy or something).
