Because some of us actually believe that it's unethical to release software to users that they are not 100% free to use and modify in any conceivable way.
Too many people today are hung up on "open source" or "free software" as a marketing bullet point. It's actually a philosophy and ideology, and the software licenses that came out of it are side effects.
The extremist stance "free as in beer from day 1" is an ideology that, it should have become clear by now, is actually hurting the freedom of the public at large, who is pushed into proprietary cages set up by ruthless profit-maximizing businesses. There should be a better way where developers are paid, high quality software gets written, and users are free. There is nothing fundamental preventing such a world to exist.
Nothing except human nature. Ethics, business ethics particularly, is empirical. Usury was a bad word for most of human history. Now we just call it financing.
If only for forward progress's sake, one should accommodate human nature, not catechize it.
But I can't modify Coca-Cola or KFC's eleven herbs and spices either.
It's called intellectual property, and it's undergirded economies both West and East since ancient times.
Intellectual property is a fiction. It is an abstraction invented whole cloth be legislative bodies to protect specific industries.