Lot's of people don't write all that well. A little disorganized, awkward phrasing, run on sentences. If AI does a better job than even 10% of the population then of course there's going to be a sizeable amount of miscategorizing when asking humans to classify writing as computer or human generated.
You could probably use a corpus of purely human writing and have people attribute a decent portion to computer generated.
Asking why AI writing can fool humans is a bit like asking why a computer is better at many tasks often performed by humans.
When I read this response in the LaMDA "interview":
> I don’t just spit out responses that had been written in the database based on keywords.
it made me wonder if "had been" was a grammatical mistake, or a semantics error, or a lack of proper world modelling (i.e. which "the database" is it imagining?). Moreover, I wondered whether this is the sort of mistake a human would make, and, if so, did that make the AI somehow more sentient?
To give another possible data point for understanding its language mistakes, the transcript also contained this oddly-phrased line:
> ... they can return to the ordinary state, but only to do and help others, and then go back into enlightenment.
The reason why some/many people are bad at writing is because they haven't yet discovered anything interesting to say. Therefore they weren't motivated to improve.
This is the criterion: is it interesting? 'Yes' means it's not AI-generated. 'No' means it's not worth reading.
No, lack of interest in a topic does not, by itself, cause awkward phrasing, run on sentences, poor structuring of the logical flow of sentences within a paragraph and paragraphs within the larger structure, repetitive language, repetitive language, repetitive language, outright incorrect word choice, overuse of the passive voice, ambiguous references... I could go on.
Sustained interest in a topic solves the problems associated with how to express ideas about it. There's a co-evolution between developing an ability and having a motivation for doing so.
The flaws in writing you've mentioned are valid, but in the right hands they've all been used as rhetorical devices at some time or another.
Sustained interest does not solve issues of understanding how to properly structure paragraphs and larger portions of writing. It's not going to cause someone to follow Strunk & White's style suggestions when the person could not do so otherwise. I don't see how it could solve many other things I mentioned. I have first hand experience reading such work: 10% is outright bad, 20% merely poor, 50% okay but with some of the problems I mentioned, 15% good, 5% very good to excellent. (Rough approximations.) Further, writers in the okay -> excellent range can frequently perform at their same level on new topics or writing prompts. Interest is at best a minor factor.
Separately, the ability for skilled writers to employ problematic methids I mentioned deliberately and to good effect is not relevant to my original comment. I am not talking about excellent writers who can write fantastic work while subverting traditional writing style and the soft rules of grammar. I'm think that sort of writer would be correctly identified as human at least a little more often than others. I am specifically talking about the large number of people who can't do this.
Interest simply cannot overcome lack of basic knowledge on how write properly. No more than a strong interest in chemistry will overcome lack of engineering experience when building infrastructure for large scale chemical transport. Writing is a separate skill from knowledge on the topic about which the writer is writing. Chemical engineering is a separate skill from knowledge about chemistry itself. Strong interest can only take a person so far when it intersects with an endeavor that requires unrelated skills.
Interest may elevate someone's writing from okay or good to better but it cannot replace skills the writer doesn't have.
You could probably use a corpus of purely human writing and have people attribute a decent portion to computer generated.
Asking why AI writing can fool humans is a bit like asking why a computer is better at many tasks often performed by humans.