As hhh already said, it was free for a long time. In addition it costs a fortune to run their models. They've mentioned as much on twitter a few times now.
Their compute is provided by Microsoft and they've got investors but even with the new premium plan its extremely unlikely they are making anything close to enough to cover their costs.
Eventually OpenAI will likely be absorbed by Microsoft as they are betting heavily on their tech and have made waves about significant investments followed by a significant ownership stake.
At $0.0003 per word (will be more with GPT-4 as its a model that requires more resources to run) their costs were over $100K per day back in December. Given how much it's taken off since then we're likely into well over $1 million per day now. The subscription service obviously isnt going to make that much for a long, long time, if ever.
In 2021 they lost over $500 million as well so Microsofts $10bn investment will cover them for a few years but will take some doing to recoup.
