They aren't. Look it up in the dictionary.

https://www.dictionary.com/browse/business

Someone's profession (their "business") can certainly be working at a nonprofit, but that's because they are getting paid. The nonprofit organization itself is not a business. You might be looking for the word "corporation", which can include nonprofits.

I don't need to look it up because I've started two nonprofits and more than a dozen corporations.

Nonprofits in the US literally are corporations, just with a different tax status. They need revenue that exceeds their costs. Many of them sell things. They can even turn a profit. Ikea operates as a nonprofit in the US.

I know nonprofits are corporations. That’s what I already said. You claimed they were businesses, which is incorrect and which I disputed.

Requiring more revenue than costs does not a business make. You starting a nonprofit does not give you special insight into the meaning of words. I am the treasurer on the board of a nonprofit. I have had to go through the books, confirm we’ve got enough cash for a year of runway, etc. The understanding of what nonprofits do is not the issue.