Not to speak for them, but for me, the answer is because a huge part of role-playing is the interaction pillar of the game. Intelligence, wisdom, and charisma have a much bigger impact on how your character speaks, interacts, and presents themselves--all things key to roleplaying that PC. What does strength, dex, and con do? "Argor flexes his muscles. Again. At everyone. All the time."?
"Aaron flexes himself out of the room."
But no, I absolutely agree with you that interaction is a huge part of roleplaying. That is key and vital. Like I know I'm talking almost purely about mechanics in this thread, but I would not play this game if it weren't for legitimate roleplaying. My favorite parts of a session are almost never combat and I love just talking to NPCs and exploring and investigating the world.
Where I disagree here is that while the mental stats admittedly would have a larger impact on that than the physical, I feel like there's so much more to your character than your stats. There's an entire chapter in 5e on character backgrounds with motivations and histories and personality.
That's where I think roleplaying needs to come from and tie to, not just how much int you have. And in that light, I feel like
all of the stats should ultimately be mostly unrelated to any actual roleplaying because your levels of intelligence, wisdom, and charisma are so much less important than
who your character is. The Sage background doesn't have an intelligence requirement. You can be a Soldier without any significant strength. You can have 8 int and still have a bunch of witty quips memorized to pass out as needed. Just because you have 8 strength doesn't mean you don't want to grab and pummel the man who killed your family. Your attributes are all pointless when compared to true character motivations and training.
I tried to deal with this difficulty in
post #28. Okay, it was tongue-in-cheek, but it had a serious message.
The trouble with dice-rolling mechanics is that they are entirely
destructive of ideas. When a player decides that his PC 'decides' to carry out a plan or execute an action, the dice may say it succeeds or fails. What the dice can't do, is come up with a better plan. That's up to the player. Not the character, the
player.
We keep going back to plans, but that's the only time I've seen intelligence requirements come up in this thread. I asked once before for examples because I couldn't think of any, but can you name a really brilliant plan from a game you were in at some point? Because completely separate from whether intelligence checks are even a good idea for planning, I don't think a situation has come up in any of my games where someone would have had to make one.
It's not semantic at all, because when you say, "It used to work this way previously", I have decades of the game period that I played where it didn't work like you described at all. 3.5 isn't the only history of the game.
And that's great that you've played so much, but previously still means "it did this once", so it could still be argued that it was a good idea where they got things right and we should go back to it. It's reasonable that I could've mentioned it was 3.5 I was talking about, but I could've really been talking about any game out there in the tone of "These guys did it this way once and I thought that was neat." It could even be some obscure homebrew thing.
I mean, if you want to give me a full rundown of how intelligence has worked in every edition of D&D I would honestly enjoy hearing that for ideas, but it's not like my post falls apart based on the D&D timeline.