Wrangling the AI to do reliable first-responses in the intro is difficult. For all my worlds' shared system prompt I use "keeping environment descriptions to a bare minimum", but the AI will still just do full environment description if you don't give it something to show the player instead. However even in my worlds which provide characters and starting event, it's probably only 80% of the time that the character interaction happens immediately in the intro (though in the remaining 20% of the time, if I just "look around" as an action, it nearly always leads to that early event.
Varies between models, even within models (with the model I've been using most (meta-llama/llama-3.3-70b-instruct:free) sometimes the responses will get into a groove that's very different from the story I want)