Ask HN: Why are so many great things free?

There seems to be an abundance of really great services that are offered free of charge, or have a free tier that fulfils my needs perfectly and offers no incentive to upgrade. Examples include Surge [0], Netlify [1], and Migadu[2], which I just discovered from the front page of HN. Why do so many services offer a really good product free of charge? Do they benefit at all, or is it about giving to the community?

[0] https://surge.sh/

[1] https://www.netlify.com/

[2] https://www.migadu.com/en/index.html