For the same reason any automation is an improvement. How many ChatGPT queries can one do in the time that it takes some rando to read a question and post a useful reply?
The real metric is the aggregation of many ChatGPT queries and iterations compared to only one Stack Exchange query.
In the case of answers that already exist on stack exchange, finding the useful one is an exercise in reading, critical thinking, copy-pasting, and testing code. It's little different form repeated queries to an AI in that sense.
It makes sense, as the results are basically Stack Exchange after it's passed through the digestive system of an AI. Whether it's human or AI, it's important to discriminate which orifice the results extrude from.