Its not 'thanking', its positive signal that GPT's previous outputs were correct, so it should continue doing whatever it was doing.
If you say no/bad etc, then GPT will try other approaches.
Is that somehow baked into the algorithms?
Are positive words of encouragement interpreted as "positive signals" by the inference pipeline? Or do they somehow influence the attention mechanism?
Because otherwise, you're just rationalizing completely random and unpredicted behavior.