Because they have too many free users that will always remain on the free plan, as they are the "default" LLM for people who don't care much, and that is a enormous cost. Also the capabilities of their paid tiers are well known to enough people that they can rely on word of mouth and don't need to demo to customers-to-be
They're not more default than people innocently googling something and getting an AI response from some form of Gemini.
Right, but that form of Gemini is also not the top Gemini model with high thinking budget that you would get to use with a subscription, the response is probably generate with Gemini Flash and low thinking.