The system mechanics for D&D are nothing if not artificial. I try not to worry too much in explaining away or justifying this particular conceit for an engine that is built primarily on artificial constructs and resolutions. There are other systems out there that are designed to address these issues, rather than making it the GMs job to do so. But since we are speaking strictly within the confines of D&D as a system, we can choose to either accept it or challenge it. Personally, I think it's unnecessary to spend an inordinate amount of effort to focus on elements that the game (and the designers themselves) spent proportionately less time concerning themselves with.
I probably chose the wrong word with "artificial". Sure, it's always artificial to turn the complexity of real life into game mechanics.
What I really meant was whether it's "real" agency or "illusory" agency.
To cite an example, in The One Ring's (1e) rules for Journeys, there is a very flavorful, Tolkien-esque subsystem for resolving mid-Journey events. Players each take a role (Hunter, Guide, Look-Out, etc.) and then use those skills to overcome the challenges.
But...they aren't really "using" those skills or making decisions. The GM ("LM") rolls dice to determine the nature of the challenge and which of those roles it targets, and then one of the players assigned to that role makes a skill check, and on a failure that character suffers the designated penalty. There's no "here's the situation, what do you want to do about it?" It's just "You have to make a skill check or lose 2 Endurance." There is absolutely zero problem-solving or decision-making. It's...well...board-gamey. (Unsurprising, since the designer made his name designing board games.).
That's what I call "illusory" agency.
This is largely a perspective of the GM. We seek ways to validate players to encourage them to play in ways that most likely suit our own preferences. And while some players might share that sentiment (usually the ones who most often feel they can 'earn' these rewards because of their innate cleverness, etc), others might expect that their efforts should be rewarded every time they do something clever, etc., and the GM is obliged to recognize such efforts with some form of compensation.
On the other hand, players who don't consider themselves to be outward, forward, or able to maintain focus during long sessions might feel something completely different. Their inability or natural tendency to remain quiet and observant in these games might feel they never get the same benefits as others who have fewer issues with expressing themselves, are more comfortable acting out, or pick up on every minute detail that the game and everyone at the table provides for them for hours at a stretch.
Given the options, a simple die roll seems much easier and less energetic than anything else that may be required of them. As far as they know, the potential rewards are identical.
The part in bold may absolutely be true. I'm definitely not talking about roleplaying, or acting, or being convincing, and still all of the above may absolutely be true. It can be risky and scary to suggest ideas in front of a group.
And I would love to find ways to encourage those sorts of players to put themselves forward more and to share their ideas and be creative. To learn to be ok with that risk.
But I, personally, don't want to make the game more algorithmically dice-dependent to cater to that tendency.
(As a side note...and this is not directed at you because I genuinely don't remember what you've said on these other topics...it seems to me this is, in some ways, a matter of 'inclusivity'. I would be very curious to see a mapping correlating what various posters have said on this particular kind of inclusivity, compared to what they have said on other inclusivity topics: orc/drow descriptions, racial bonuses, safety cards, etc. It would be interesting to see if some people use an inclusivity argument in one context, but take a "if they can't hack it they should find a new game" stance on other topics.)