Why are social skills so hard to succeed at?

Reading this example, I read it as:
“Intent: Stop him from disrupting the ritual AND Subdue him Task: Wrestling”
But part of that intent is buried in the task.

There is not anything, strictly, wrong with this rules wise. The codex on pages 111 goes through a scenario where a player’s task modifies his intent (although within the context of a negotiation to make his task make fictional sense to the GM, rather than initial statement), however I am not sure I feel this is best practice.

Best case scenario: I understand exactly what you mean, I am listening attentively and processing what you are saying correctly, I maybe ask some questions to clarify or asses difficulty. “Sounds good, vs power test.”, “Wrestling him to the ground might disrupt the magic circle, there’s an obstacle penalty to avoid that”, “This sounds like two different intents to me, how about a linked test, first power to stop him from disrupting the ritual, then brawling to pin him down”

Less than best case scenario: I’m not at my best, I had a bad day, didn’t get enough sleep, two other players are competing for my attention, whatever. I hear you state your intent, make sure I understand that. Then I shorthand your task description as “wrestling”. Then we have this conversation:

The rules say you are correct. And there is a lot of blame on me for not listening to you fully attentively, but we can’t always be at 100% in our communication. If I was the player in question, I might feel like the GM is trying to cheat me out of what the rules say I should have (my intent and task), if I was the GM in question, I might be frustrated that the additional effect of being subdued wasn’t explicitly stated, that it got by me by not being enumerated in the intent.

But being more explicit in our intents avoids this issue fairly cleanly, and makes it more clear to the whole table what happens when you win your die roll. Even if the GM DOESN’T fully understand the rules on page 30 like in your example, explicitly stating your full intent avoids that too.

Not trying to say not to go about with evocative descriptions but make sure everyone at the table knows what exactly you expect to have happen as a result of that

In the case that you explicitly KNEW you wanted to subdue him.
“My intent is to subdue him and let my friend complete the ritual. My task is to grab him in a choke hold, wrestle him to the ground, and subdue him.”
And the case where you just wanted your initial intent but the subduing came about just from how you explained your task, just ask to clarify before you roll the dice.
“My intent is to prevent him from interfering with my friend completing the ritual. My task is to grab him in a choke hold, wrestle him to the ground, and subdue him. He’d be pretty well restrained right?”