> Given that ChatGPT was just released last fall and it was expected to revolutionize practically everything, isn't it still telling that usage is falling?

Its not, though. ChatGPT, the website is basically an (increasingly non-exclusive, given BingAI) frontend. What is claimed to be revolutionary is the underlying models (in the narrow view) and similar generative AI systems (in the broader view). As more applications are built with either OpenAIs own underlying models or those from the broader space, the ChatGPT website should be expected to represent a smaller share of the relevant universe of use.