Later last year, we saw the release of GPT's text-davinci-003, and in an attempt to showcase this new model to the research community, they launched ChatGPT.
I think what we are seeing now is that chatGPT is best when it is close to existing applications. For example what 14 year old is using the chatGPT app vs the Snapchat AI Chat which uses the API internally.
The recent drop in usage could likely be attributed to such preferential shifts, further compounded by the timing of school holidays.