Open Source was made by someone. With copyleft they decided: You can use my code, you can modify my code but if you build on my work you will also open source that.

Open Source is not necessarily a business decision but often a personal one. Often authors start without any pay but instead because they thought it was a nice thing they want to share. So it's their right to say what people can or can't do with their original work.

Companies have the ability to write their own software if they don't want to follow these rules.