I'm not sure how much it has to do with LLMs.
It feels more like it was sort of a fad thing and, especially once any certification value essentially fell off the back of the truck (and therefore no one really willing to pay)--much less any real value delivered to people who weren't already autodidacts--it sort of faded away.
From where I was at the time Linkedin Learning (or whatever it was called) was a sometimes vaguely useful company benefit for random stuff but I'm not sure to what degree anyone even tracked who used it.
I think what killed all MOOC learning was that they ALL saw this giant TAM for corporate training and thought.. we have to get into that market.
That is what hollowed out the value.. all the incentives are inverse to building long term value.
Everything becomes check box driven product development to close the next "big deal" and then no development is done to really enhance the core of the system or the core value to the learner. It becauses now it morphs into can we show value to the clients/decision makers/learning admins?