The messages that are sent over Chat are ones that are needed for functionality of the Chat system on Twitch, which is why a points redemption that needs to display custom messages are sent over chat as Barry has mentioned. Any others don’t need to display things so aren’t going to be sent over Chat.
There will be some API endpoints in the future for parts of the points system, and potentially Webhook topics for those endpoints, but there have been no announced plans to add unnecessary messages about points redemptions to chat.