Evidence or not, this is probably the most satisfying explanation I've heard for this behaviour.
My own suspicion is that LLMs are not becoming more general-purpose over time, as these companies had hoped, and ongoing development in that direction is stalling. They will likely need to move in the direction of more specialization and train LLMs for specific use-cases. However, this would also be admitting that they are not on a direct path to AGI.
To be clear I do not believe it is intentional (nor do I believe I am somehow smarter or more knowledgable than the people running these processes).
I believe it is (very) unfortunately converging on the communication style that currently makes the most money as far as publicly available communication goes. Unfortunate, but not entirely unexpected.
My own suspicion is that LLMs are not becoming more general-purpose over time, as these companies had hoped, and ongoing development in that direction is stalling. They will likely need to move in the direction of more specialization and train LLMs for specific use-cases. However, this would also be admitting that they are not on a direct path to AGI.