Good question, I don't personally know. The linked article would suggest there are plenty of people working on human feedback for chatbots, but that still doesn't give us any hard numbers or any sense of how the number of people involved is changing over time. Perhaps the best datapoint I have is that revenue for SurgeAI (one of many companies that provides data labeling services to Google and OpenAI among others) has grown significantly in recent years, partly due to ScaleAI's acquisition by Meta, and is now at $1.2 billion without having raised any outside VC funding:

https://finance.yahoo.com/news/surge-ai-quietly-hit-1b-15005...

Their continued revenue growth is at least one datapoint to suggest that the number of people working in this field (or at least the amount of money spent on this field) is not decreasing.

Also see the really helpful comment above from cjbarber, there's quite a lot of companies providing these services to foundation model companies. Another datapoint to suggest the number of people working providing labeling / feedback is definitely not decreasing and is more likely increasing. Hard numbers / increased transparency would be nice but I suspect will be hard to find.