Most data vendors will require a free API key because that's their GTM. They want you to create an account with them to get a free API key and then expect to be able to upsell you over time.
Or you can access "free data" (e.g. yfinance) that relies on projects who actively scrape financial data from a website - these tend to need a lot of updates from main maintainer since there are no aligned incentives between maintainer of the scrapped API and company that has the data.
PS: I'm the main creator behind the OpenBB project on GitHub.