https://techcrunch.com/2021/05/03/duolingo-ec1-monetization/

As its meandering route to monetization will demonstrate, Duolingo isn’t mission-oriented, it’s mission-obsessed.

Co-founders Luis von Ahn and Severin Hacker never wanted to charge consumers for access to Duolingo content, a purpose imbued throughout the company’s culture. For years in order to work at Duolingo, you had to be comfortable with joining a company in Pittsburgh that was in no rush to make money. The startup, filled with education enthusiasts and mission-driven employees, became “very college pizza vibes,” Gina Gotthilf, former VP of Marketing at Duolingo, described. Everyone was against making money and having structure — some employees even threatened to quit if Duolingo ever charged a cent to users.