Because it provides value. It generates answers for questions that can require a more extensive due dilligence. Instead of a human scouring the internet for answers it can directly and comprehensively answer the question in the context is asked with explanations. For instance, software developers are using it by being recommended actual implementations in code that actually works, solving problems much faster and being more productive.

Edit: I want to add that the answers are very specific to the problem stated by the user. ChatGPT does not provides a general answer but a very specific answer for the problem at hand.