Fundamentally in a game which simplifies the complexity of combat into turn-taking rounds; movement; to-hits; and damage rolls is going to have some dissonance between it and the real world where everyone is moving at once; heat, vision limitations, and fatigue exist; and combat strategies vary from not being where an opponent is thrust, trying to bypass armor by hitting them where it doesn't cover, and powering through the armor with percussive or armor-piercing weapons. Each simplification is going to have pros and cons, and different people will like different implementations, in part because there are different goals such as realism*, playability, and genre-matching.
*And, if the frequency of use of the WvsAC modifiers in oD&D/1E are any indication, there is a limit to the amount of realism regularly expected of the game.
The OP has a point -- there is some level of belief (perpetuated from everything from later-era Europeans to Bugs Bunny cartoons) that medieval fighting was guys in clunky tin cans whaling on each other with vaguely sharpened metal bars. That's one extreme. At the same time, there seems to be (maybe just in gaming/fantasy-adjacent Youtube circles) of people wanting to pat themselves on the back for knowing otherwise, and these can often overreach. As pointed out, doing gymnastics or generally being agile in blue jeans is harder than in exercise gear*. A max-Dex for heavy armor isn't really unreasonable, it's just shouldn't only be for heavy armor -- doing so with a bunch of camping gear or 150 lbs of looted coins or the bard's instrument collection should also apply penalties, and these are often ignored (or at least obviated by the encumbrance rule, in that a high-strength character can have no penalty for total weight carried, but still has it for the armor they are wearing, etc.).
*discussion about 'light' armors to follow
I saw some others pointing out genre emulation and some pushback on it, and I think the former have the right of it. The game has always been (and has been moving more in this direction since 2e, if not earlier) one where some character wants to be unarmored (the monk, I'm assuming wizards would want armor if they could), some want to be wearing light armor* (thieves, sometimes rangers), and some want as heavy as they can carry/afford. That certainly doesn't have to be the case. In AD&D it was generally best to get as heavy armor as your class allowed*. However, if you make that decision, it becomes really hard to justify playing a swashbuckler, it is hard to make a thief class enjoyable, high-seas adventure or other places where the heavy armor comes off changes a lot of dynamics, and a bunch of other little issues. Maybe that's not a problem for some groups, but for others it is and I think that had something to do with the design choice.
*although, as pointed out, basic-classic and AD&D had speed maxes for certain armors
An overarching point here also comes to mind. D&D characters don't do what historical people who wore armor and wielded weapons tended to do. They wander the countryside, often in-armor most of the time, often with few if any attendants and minimal baggage trains or camp followers or the like, to climb into conveniently places caverns or abandoned structures in search of treasure, often fighting monsters against which real world arms and armor were not designed. Realistically (given the unrealistic premise), whole new types of arms and armor would have evolved to face these challenges, just like castles would have not evolved as they did* if deadly flying creatures were a real concern. We'd see armor that is lighter, probably easier to repair, and definitely easier to transport. Suddenly, being the opponent-at-their-base, especially with pre-knowledge of time of engagement, becomes a huge advantage. That they can have all the heaviest and least convenient armor while the (presumably) PCs are traipsing around in their transit-armor. This could be an interesting notion for a specific worldbuilding. However, I can see why WotC or anyone else wouldn't think that overly marketable. Anyways, my point is that 'but realism' in the end runs into the issue that D&D adventuring isn't realistic, so any given decision is going to be a tradeoff of which unrealism you personally can or can't accept.
*certainly more ballistae and maybe even whole-keep roofs
Regarding light armors -- yes, for the most part this is a misnomer. Regardless of material, people have tended to wear about the same amount of weight of armor whether it was plate, mail, gambeson, or (when really worn) leather. There were lighter armors, but mostly for specific reasons (simple mail shirt for accessibility, some kind of hidden armor for dueling perhaps, and of course any compromise made for naval or hot-environments). The question becomes -- if someone wants to play a dashing rogue with a light level of armor protection, regardless of historical accuracy, is that a bad thing? I don't find a single clear correct answer on that.
Regarding gamist/playability concerns. AD&D was really good at rewarding success with further success. Good starting rolls made you really good at advancing and continuing to get things better than characters with lower starting rolls. An AD&D fighter with 18+ Str, and fair-good Dex and Con (or, let's be honest, fair-good Dex and Con and gauntlets of ogre power, which were common enough) started out winning and it just keep cascading (compared to the PCwith more moderate rolls). I think 3e wanted to limit how much you needed to have a really good Str, Dex, and Con in order to be good at being a fightery type. Given how everyone needed Good Dex and Con (and Wis) for saves, how fighters were still hugely more MAD than casters, and how mithral plate meant you were still shooting for a 16 Dex, I'd say their implementation left a lot to be desired. Still I understand the motivation, if that is what it was.
Sorry about the random order here, these were just my thoughts as they came. Hope someone finds them helpful.