Multiple reasons probably:

1. Less context window to work with.

2. Things were "different" in the early days. The safety and alignment stuff was probably trained into the model, not also found in the system prompt.

3. Safety and alignment meant something different 3 years ago. Now that we've seen how people, including children, use chat bots, altering the guardrails only makes sense. Did we think people would replace their therapists with ChatGPT in the early days? No. Do we know now that they will? Yes.