At the moment they're in the "get people used to us" phase still, reasonable rates, people get more than their money's worth out of the service, and as another commenter pointed out, ChatGPT is a household name unlike Grok or Gemini or the other competition thanks to being the first mover.
However, just like all the other disruptive services in the past years - I'm thinking of Netflix, Uber, etc - it's not a sustainable business yet. Once they've tweaked a few more things and the competition has run out of steam, they'll start updating their pricing, probably starting with rate limits and different plans depending on usage.
That said, I'm no economist or anything; Microsoft is also pushing their AI solution hard, and they have their tentacles in a lot of different things already, from consumer operating systems to Office to corporate email, and they're pushing AI in there hard. As is Google. And unlike OpenAI, both Microsoft and Google get the majority of their money from other sources, or if they're really running low, they can easily get billions from investors.
That is, while OpenAI has the first mover advantage, ther competitions have a longer financial breath.
(I don't actually know whether MS and Google use / licensed / pay OpenAI though)