Let me tell you a parable.
There was a student who was given as assignment of writing an essay. The student found 10 similar essays online. He copied selected bits of different essays. He tediously reworded the result, removed some sentences, added some adjectives and adverbs, shifted some more sentences, added some glue — all with the single-minded goal of covering up the tracks. Eventually, a voluminous essay was complete.
The student has put a lot of effort into this; possibly even more that if he had written it himself. He did learn a bit about essays, though he didn't really practice writing one. He did practice some skills that would be useful in a future bullshit job, though. The essay passes all #plagiarism checks, even though it immediately raises red flags to any human reading it: the sudden style changes, contradictory statements, sentences that don't make much sense in their context. And if he was asked to defend it, he might be in trouble.
So, the student put an effort (though not the right kind of effort), produced a mediocre essay and learned something (though bullshit skills rather than creative skills). Now let's consider a different situation: rather than doing all that himself, the student paid somebody else to do it; and not to *write* an original essay, but to do all the shenanigans described above.
That's precisely what using LLMs is. You tell them to write an essay, so they find and mix random stuff, and produce a mediocre essay. You don't put an effort, you don't learn anything, perhaps you don't even read "your" essay. And it passes all the plagiarism checks.
